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OAK  S  i.  nUor  .. 

THE  UNIVERSITY 


OF  ILLINOIS 


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INTERNATIONAL 
LIBRARY  of  TECHNOLOGY 


A  SERIES  OF  TEXTBOOKS  FOR  PERSONS  ENGAGED  IN  THE  ENGINEERING 
PROFESSIONS  AND  TRADES  OR  FOR  THOSE  WHO  DESIRE 
INFORMATION  CONCERNING  THEM.  FULLY  ILLUSTRATED 
AND  CONTAINING  NUMEROUS  PRACTICAL 
EXAMPLES  AND  THEIR  SOLUTIONS 


SANDS  AND  CEMENTS 
PLAIN  CONCRETE 
BUILDING  STONE  AND  BRICK 
ELEMENTS  OF  STONE  MASONRY 
ELEMENTS  OF  BRICK  MASONRY 
FIELD  OPERATIONS  AND  CONCRETE  WORK 

TESTS  ON  CEMENT 
CONCRETE  BUILDING  BLOCKS  - 
HEAVY  FOUNDATIONS 
PILING 

STEEL  AND  OTHER  METALS 
LOADS  IN  STRUCTURES  ' 

INSURANCE  ENGINEERING 
WATERPROOFING  OF  CONCRETE 


SCRANTON: 

INTERNATIONAL  TEXTBOOK  COMPANY 


108 


Sands  and  Cements:  Copyright,  1909,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 

Plain  Concrete:  Copyright,  1906,  1909,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 

Building  Stone  and  Brick:  Copyright,  1904,  1909,  by  International  Textbook  Com¬ 
pany.  Entered  at  Stationers’  Hall,  London. 

Elements  of  Stone  Masonry:  Copyright,  1898,  by  The  Colliery  Engineer  Company. 
Copyright,  1907,  1909,  by  International  Textbook  Company.  Entered  at  Sta¬ 
tioners’  Hall,  London.  • 

Elements  of  Brick  Masonry:  Copyright,  1898,  1899,  by  The  Colliery  Engineer 
Company.  Copyright,  1907,  1909,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 

Field  Operations  and  Concrete  Work:  Copyright,  1910,  by  International  Textbook 
Company.  Entered  at  Stationers’  Hall,  London. 

Tests  on  Cement:  Copyright,  1910,  by  International  Textbook  Company.  Entered 
at  Stationers’  Hall,  London. 

Concrete  Building  Blocks:  Copyright,  1910,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 

Heavy  Foundations:  Copyright,  1904,  1910,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 

Piling:  Copyright,  1910,  by  International  Textbook  Company.  Entered  at  Sta¬ 
tioners’  Hall,  London. 

Steel  and  Other  Metals:  Copyright,  1906,  1909,  by  International  Textbook  Com¬ 
pany.  Entered  at  Stationers’  Hall,  London. 

Loads  in  Structures:  Copyright,  1904,  1909,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 

Insurance  Engineering:  Copyright,  1910,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 

Waterproofing  of  Concrete:  Copyright,  1910,  by  International  Textbook  Company. 
Entered  at  Stationers’  Hall,  London. 


All  rights  reserved. 


24853 


108 


PREFACE 


The  International  Library  of  Technology  is  the  outgrowth 
of  a  large  and  increasing  demand  that  has  arisen  for  the 

r 

Reference  Libraries  of  the  International  Correspondence 
Schools  on  the  part  of  those  who  are  not  students  of  the 
Schools.  As  the  volumes  composing  this  Library  are  all 
printed  from  the  same  plates  used  in  printing  the  Reference 
Libraries  above  mentioned,  a  few  words  are  necessary 
regarding  the  scope  and  purpose  of  the  instruction  imparted 
to  the  students  of — and  the  class  of  students  taught  by — 
these  Schools,  in  order  to  afford  a  clear  understanding  of 
their  salient  and  unique  features. 

The  only  requirement  for  admission  to  any  of  the  courses 
offered  by  the  International  Correspondence  Schools,  is  that 
the  applicant  shall  be  able  to  read  the  English  language  and 
to  write  it  sufficiently  well  to  make  his  written  answers  to 
the  questions  asked  him  intelligible.  Each  course  is  com¬ 
plete  in  itself,  and  no  textbooks  are  required  other  than 
those  prepared  by  the  Schools  for  the  particular  course 
selected.  The  students  themselves  are  from  every  class, 
trade,  and  profession  and  from  every  country;  they  are, 
almost  without  exception,  busily  engaged  in  some  vocation, 
and  can  spare  but  little  time  for  study,  and  that  usually 
outside  of  their  regular  working  hours.  The  information 
desired  is  such  as  can  be  immediately  applied  in  practice,  so 
that  the  student  may  be  enabled  to  exchange  his  present 
vocation  for  a  more  congenial  one,  or  to  rise  to  a  higher  level 
in  the  one  he  now  pursues.  Furthermore,  he  wishes  to 
obtain  a  good  working  knowledge  of  the  subjects  treated  in 
the  shortest  time  and  in  the  most  direct  manner  possible. 

iii 


343C03 


IV 


PREFACE 


In  meeting  these  requirements,  we  have  produced  a  set  of 
books  that  in  many  respects,  and  particularly  in  the  general 
plan  followed,  are  absolutely  unique.  In  the  majority  of 
subjects  treated  the  knowledge  of  mathematics  required  is 
limited  to  the  simplest  principles  of  arithmetic  and  mensu¬ 
ration,  and  in  no  case  is  any  greater  knowledge  of  mathe¬ 
matics  needed  than  the  simplest  elementary  principles  of 
algebra,  geometry,  and  trigonometry,  with  a  thorough, 
practical  acquaintance  with  the  use  of  the  logarithmic  table. 
To  effect  this  result,  derivations  of  rules  and  formulas  are 
omitted,  but  thorough  and  complete  instructions  are  given 
regarding  how,  when,  and  under  what  circumstances  any 
particular  rule,  formula,  or  process  should  be  applied;  and 
whenever  possible  one  or  more  examples,  such  as  would  be 
likely  to  arise  in  actual  practice — together  with  their  solu¬ 
tions — are  given  to  illustrate  and  explain  its  application. 

In  preparing  these  textbooks,  it  has  been  our  constant 
endeavor  to  view  the  matter  from  the  student’s  standpoint, 
and  to  try  and  anticipate  everything  that  would  cause  him 
trouble.  The  utmost  pains  have  been  taken  to  avoid  and 
correct  any  and  all  ambiguous  expressions — both  those  due 
to  faulty  rhetoric  and  those  due  to  insufficiency  of  statement 
or  explanation.  As  the  best  way  to  make  a  statement, 
explanation,  or  description  clear  is  to  give  a  picture  or  a 
diagram  in  connection  with  it,  illustrations  have  been  used 
almost  without  limit.  The  illustrations  have  in  all  cases 
been  adapted  to  the  requirements  of  the  text,  and  projec¬ 
tions  and  sections  or  outline,  partially  shaded,  or  full-shaded 
perspectives  h'ave  been  used,  according  to  which  will  best 
produce  the  desired  results.  Half-tones  have  been  used 
rather  sparingly,  except  in  those  cases  where  the  general 
effect  is  desired  rather  than  the  actual  details. 

It  is  obvious  that  books  prepared  along  the  lines  men¬ 
tioned  must  not  only  be  clear  and  concise  beyond  anything 
heretofore  attempted,  but  they  must  also  possess  unequaled 
value  for  reference  purposes.  They  not  only  give  the  maxi¬ 
mum  of  information  in  a  minimum  space,  but  this  infor¬ 
mation  is  so  ingeniously  arranged  and  correlated,  and  the 


PREFACE 


v 


indexes  are  so  full  and  complete,  that  it  can  at  once  be 
made  available  to  the  reader.  The  numerous  examples  and 
explanatory  remarks,  together  with  the  absence  of  long 
demonstrations  and  abstruse  mathematical  calculations,  are 
of  great  assistance  in  helping  one  select  the  proper  for¬ 
mula,  method,  or  process  and  in  teaching  him  how  and 
when  it  should  be  used. 

This  volume  is  devoted  principally  to  a  description  of 
stone  and  brick  masonry  and  plain  concrete.  It  also 
embraces  the  allied  subjects  of  heavy  foundations  and  piling. 
The  text  is  so  complete  and  the  details  so  numerous  that 
such  a  treatise  can  hardly  be  found  in  one  volume  elsewhere. 
Special  attention  has  been  given  to  the  waterproofing  of 
concrete.  The  subject  of  concrete  building  blocks  has  been 
exhaustively  treated  from  the  standpoint  of  the  block  manu¬ 
facturer  and  the  small  contractor  who  is  about  to  embark  in  the 
block  business.  This  volume  should  therefore  prove  useful 
to  both  the  contractor  and  the  architect.  As  it  forms  the 
basis  for  information  on  reinforced  concrete,  it  will  be  found 
valuable  if  used  in  connection  with  volumes  of  this  library 
that  relate  to  that  subject. 

The  method  of  numbering  the  pages,  cuts,  articles,  etc.  is 
such  that  each  subject  or  part,  when  the  subject  is  divided 
into  two  or  more  parts,  is  complete  in  itself;  hence,  in  order 
to  make  the  index  intelligible,  it  was  necessary  to  give  each 
subject  or  part  a  number.  This  number  is  placed  at  the  top 
of  each  page,  on  the  headline,  opposite  the  page  gumber; 
and  to  distinguish  it  from  the  page  number  it  is  preceded  by 
the  printer’s  section  mark  (§).  Consequently,  a  reference 
such  as  §  16,  page  26,  will  be  readily  found  by  looking  along 
the  inside  edges  of  the  headlines  until  §16  is  found,  and 
then  through  §16  until  page  26  is  found. 

International  Textbook  Company 


CONTENTS 


Sands  and  Cements  Section  Page 

Cementing  Materials . 29  1 

Limes . 29  2 

Cements . 29  G 

Miscellaneous  Cementing  Materials  ...  29  12 

Sand  and  Its  Mixtures . 29  14 

Mortars . 29  18 

Plain  Concrete 

Materials  Used  in  Concrete . 30  1 

Cement  Mortar . 30  2 

Aggregates  Other  Than  Sand . 30  3 

Proportioning  of  Ingredients  ......  30  15 

Properties  of  Concrete .  30  20 

Working  Stresses  and  Strength  Values  of 

Concrete  .  30  24 

Concrete  Mixtures  .  . .  30  29 

Working  of  Concrete .  30  33 

Building  Stone  and  Brick 

Physical  Properties  of  Building  Stone  .  .  31  1 

Classification  of  Building  Stone . 31  5 

Durability  of  Building  Stone . 31  14 

Selection  of  Building  Stones . 31  22 

Clay  Brick . 31  30 

TerraCotta . 31  37 

Sand-Lime  Brick . 31  38 

Size  and  Strength  of  Brick . 31  39 


m 


IV 


CONTENTS 


Elements  of  Stone  Masonry  Section  Page 

Stone-Cutting  Tools . 32  1 

Finish  of  Stonework  . . 32  5 

Rubblework . 32  17 

Ashlar .  32  21 

Care  of  Stonework .  32  28 

Trimmings . ' .  32  31 

Footings .  32  43 

Thickness  of  Walls  .  32  54 

Sidewalks .  32  55 

Elements  of  Brick  Masonry 

Methods  of  Laying  Brick . 33  1 

Bond  in  Brickwork . 33  4 

Difficulties  in  Bricklaying . 33  14 

Thickness  of  Brick  Walls . 33  15 

Walls  for  Dwelling  Houses . 33  16 

Walls  for  Warehouses . 33  19 

Types  of  Brick  Walls .  33  28 

Field  Operations  and  Concrete  Work 

Duties  of  the  Superintendent  ......  34  1 

Handling  of  Materials . 34  5 

Materials  Used  in  Concrete  Work  ....  34  8 

Devices  Used  in  Concrete  Construction  .  34  10 

Batch  Mixers . 34  11 

Continuous  Mixers . 34  19 

Quantitative  Mixers .  34  24 

Power  Equipment  for  Mixers .  34  27 

Hand-Cart  Mixers .  34  29 

Operation  of  Mixers .  34  31 

Hauling  Devices .  34  34 

Hoisting  Devices  .  .  .  • .  34  37 

Combined  Hoisting  and  Mixing  Devices  .  .  34  43 

Tools  Used  in  Placing  Concrete .  34  47 

Machinery  for  Bending  Steel .  34  48 

Notes  for  the  Superintendent  ......  34  51 

Finish  of  Concrete .  34  53 


CONTENTS 


v 

Tests  on  Cement  Section  Page 

Field  Inspection . 35  1 

Sampling . 35  3 

Primary  Tests . 35  5 

Tensile  Strength . 35  14 

Secondary  Tests .  35  24 

Fineness  . 35  27 

Specific  Gravity  . .  35  32 

Chemical  Analysis .  35  34 

Natural  and  Slag  Cements .  35  36 

Specifications .  35  36 

Concrete  Building  Blocks 

Manufacture  of  Concrete  Blocks . 36  4 

Essential  Qualities  of  Concrete  Blocks  .  .  36  12 

Factors  Affecting  the  Quality  of  Blocks  36  17 

Materials  of  Manufacture . 36  IS 

Manufacturing  Processes .  36  21 

Arrangement  and  Equipment  of  Factory  .  36  39 

Footings  and  Foundations . 37  1 

Laying  and  Fitting  of  Concrete  Blocks  .  .  37  2 

Wall  Construction . 37  4 

jCauses  of  Failures  in  the  Block  Industry  .  37  9 

Cost  of  Concrete  Blocks . 37  10 

Specifications . 37  13 

Heavy  Foundations 

Single  Footings . 38  1 

Compound  Footings .  38  20 

Rectangular  Footings .  38  20 

Fan-Shaped  Footings .  38  35 

Details  of  Cantilever  Foundations  ....  38  44 

Design  of  Cantilever  Foundations  ....  38  50 

Piling 

Varieties  of  Piles . 39  1 

Wooden  Bearing  Piles . 39  2 

Sand  Piles . 39  13 

Metal  Bearing  Piles . 39  14 

SheetPiles . 39  16 


VI 


CONTENTS 


Piling — Continued  Section  ■  Page 

Methods. of  Driving  Piles . 39  23 

Strength  of  Piles .  39  29 

Concrete  Piling .  39  35 

Construction  and  Driving  of  Concrete  Piles  39  42 

Special  System  of  Concrete  Foundations  39  57 

Cost  of  Concrete  Piles .  39  59 

Strength  and  Reinforcement  of  Piles  .  .  .  39  02 

Reinforced-Concrete  Sheet  Piling  ....  39  05 

Steel  and  Other  Metals 

Production  of  Iron . 40  2 

Cast  Iron  . 40  5 

Wrought  Iron . 40  7 

Manufacture  of  Steel . 40  10 

Blister  Steel  and  Shear  Steel . 40  14 

Alloy  Steels . 40  15 

Copper,  Zinc,  and  Alloys . 40  17 

Loads  in  Structures 

Floor,  Roof,  and  Wind  Loads . 41  1 

Dead  Load . 41  1 

Live  Load . 41  13 

Snow  and  Wind  Loads . 41  *  27 

Disposition  of  Loads . 41  35 

Insurance  Engineering 

Purpose  of  Fire  Insurance . 42  1 

Cause  and  Prevention  of  Fires . 42  2 

Extinguishment  of  Fires . 42  14 

Adjustment  of  Insurance  Rates . 42  16 

Limits  of  Insurance . 42  18 

Waterproofing  of  Concrete 

Requirements  of  Waterproofing .  42  21 

Classification  of  Systems .  42  23 

Integral  Method  of  Waterproofing  ....  42  25 

Superficial  Method  of  Waterproofing  ...  42  29 

Membrane  Method  of  Waterproofing  ...  42  32 

Roof  Waterproofing .  42  35 

Subsurface  Waterproofing .  42  41 


CEMENTING  MATERIALS 


INTRODUCTION 

1.  Definitions. — Any  substance  that  becomes  plastic 
under  certain  treatment  and  subsequently  reverts  to  a  tena¬ 
cious  and  inelastic  condition  may,  in  a  broad  sense,  be  termed 
a  cement.  However,  nearly  all  the  cementing  materials 
that  are  employed  in  building  construction  are  obtained  by 
the  heating,  or  calcination ,  as  it  is  called,  of  minerals  composed 
wholly  or  in  part  of  lime.  The  different  composition  of  these 
minerals,  as  well  as  the  properties  of  the  calcined  products, 
enables  the  various  resulting  substances  to  be  classified  as 
limes ,  hydraulic  cements ,  plasters ,  and  miscellaneous  cements. 
Although  all  these  materials  have  cementing  properties,  the 
term  cement  is  commonly  used  to  apply  only  to  the  group 
made  up  of  hydraulic  cements,  hydraulic  meaning  that  these 
substances  possess  the  ability  to  set.  or  become  hard,  under 
water. 

2.  Uses  of  Cementing  Materials. — Cementing  mate¬ 
rials,  in  building  construction,  have  three  principal  uses, 
namely,  (1)  as  materials  to  hold  other  bodies  together;  (2)  as 
materials  with  which  to  coat  parts  of  structures;  and  (3)  as 
building  materials  in  themselves.  The  first  use  is  illustrated 
by  the  mortar  in  the  joints  between  stone  and  brick;  the 
second,  by  a  plastering  material  to  coat  walls;  and  the  third, 
by  concrete  footings,  walls,  piers,  pavements,  etc. 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS'  HALL,  LONDON 

§  29 


211—2 


2 


SANDS  AND  CEMENTS 


§29 


3.  Classification  of  Lames  and  Hydraulic  Cements. 

Limes  and  hydraulic  cements  (which  will  hereafter  be 
called  simply  cements)  are  composed  essentially  of  oxide 
of  calcium,  or  lime,  generally  called  quicklime ,  with  which 
may  be  combined  certain  argillaceous,  or  clayey,  elements, 
notably  silica  and  alumina,  it  being  to  these  elements  that  the 
hydraulic  properties  of  certain  of  these  materials  are  due. 
The  quantity  of  silica  and  alumina  present  in  these  substances 
enables  them  to  be  classified  as  common  limes ,  hydraulic  limes , 
and  cements. 

The  ratio  of  the  quantity  of  silica  and  alumina  present  in 
these  materials  to  the  quantity  of  lime  is  called  the  hydraulic 
index.  In  common  limes,  this  index  is  less  than  iW;  in 
hydraulic  limes,  it  lies  between  -nr0“  and  and  in  cements, 
it  exceeds  ToV  These  limes  merge  into  each  other  so  gradually, 
however,  that  it  is  often  difficult  to  distinguish  the  dividing 
line  between  them. 


LIMES 


CLASSIFICATION  OF  LIMES 

4.  The  commercial  varieties  of  lime  may  be  classified  as 
common,  hydrated,  and  hydraulic.  The  common  limes,  also 
called  quicklimes ,  may  be  subdivided  into  rich,  or  jat,  lime , 
and  meager,  or  poor,  lime. 

5.  Common  Limes.— The  grade  of  common  lime  known 
as  fat,  or  rich,  lime  is  almost  pure  oxide  of  calcium, 
CaO,  and  contains  only  about  5  per  cent,  of  impurities.  It 
has  a. specific  gravity  of  about  2.3  and  a  great  affinity  for 
water,  of  which  it  absorbs  about  one-quarter  of  its  weight. 
This  absorption  is  accompanied  by  a  great  rise  in  temperature, 
by  the  lime  bursting,  and  by  the  giving  off  of  vapor.  The 
lime  finally  crumbles  to  a  powder.  This  powder  occupies 
from  two  and  one-half  to  three  and  one-half  times  as  much 
volume  as  the  original  lime,  the  exact  amount  depending  on 
its  initial  purity.  When  the  lime  is  in  this  plastic  state,  it  is 


§  29 


SANDS  AND  CEMENTS 


3 


said  to  be  slaked.  It  is  then  unctuous  and  soft  to  the  touch, 
and  from  this  peculiarity  it  derives  the  name  of  fat  or  rich. 

6.  Meager,  or  poor,  lime  consists  of  from  60  to  90  per 
cent,  of  pure  lime,  the  remainder  being  impurities,  such  as 
sand  or  other  foreign  matter.  These  impurities  have  no 
chemical  action  on  the  lime,  but  simply  act  as  adulterants. 
Compared  with  fat  lime,  poor  lime  slakes  more  slowly  and 
evolves  less  heat.  The  resulting  paste  is  also  thinner  and  not 
so  smooth,  greatly  resembling  fat  slaked  lime  mixed  with  sand. 
Poor  lime  is  not  so  good  for  building  purposes  as  fat  lime,  nor 
has  it  such  extensive  use. 

¥  7.  Hydrated  Lime. — The  class  of  lime  called  hydra¬ 

ted  lime  (calcium  hydrate)  is  merely  thoroughly  slaked 
fat  lime  in  the  form  of  a  fine  powder,  Ca(OH) 2.  It  is 
used  extensively  in  conjunction  with  cement  for  making 
mortar,  and  also  in  the  sand-lime  brick  industry. 

8.  Hydraulic  Himes. — Limes  that  contain  enough 
quicklime  to  slake  when  water  is  added,  and  enough  clay  or 
sand  to  form  a  chemical  combination  when  wet,  thus  giving 
them  the  property  of  setting  under  water,  are  called  hydrau¬ 
lic  limes. 

Limes  of  this  class  are  made  by  burning  limestones  con¬ 
taining  from  5  to  30  per  cent,  of  clay  or  sand.  They  are  often 
considered  as  divided  into  three  classes,  namely,  feebly 
hydraulic ,  ordinarily  hydraulic ,  and  eminently  hydraulic ,  in 
proportion  to  the  quantity  of  argillaceous  materials  present. 
The  slaking  qualities  vary  from  slaking  in  a  few  minutes  with 
considerable  heat  after  water  is  added,  in  the  feebly  hydraulic, 
to  slaking  only  after  many  hours,  with  practically  no  evolution 
of  heat  and  without  cracking  or  powdering,  in  the  eminently 
hydraulic.  The  time  of  setting  under  water  also  varies  from 
setting  as  hard  as  soap  in  2  years,  with  the  feebly  hydraulic, 
to  becoming  as  hard  as  stone  in  3  or  4  days,  with  the  eminently 
hydraulic.  If  carbonate  of  magnesia  is  present  in  the  lime, 
it  reduces  the  energy  of  the  slaking,  but  increases  the  rapidity 
of  the  setting  and  the  ultimate  strength  when  set. 


4 


SANDS  AND  CEMENTS 


§29 


As  the  quantity  of  clay  is  increased,  hydraulic  lime  gradu¬ 
ally  merges  into  hydraulic  cement,  so  that  it  is  often  difficult 
to  determine  whether  a  material  about  on  the  border  line  is 
a  lime  or  a  cement.  Hydraulic  limes,  however,  are  but  little 
used  in  the  United  States,  their  place  being  taken  by  natural 
cement.  These  limes,  therefore,  will  not  be  discussed  further 
in  this  Section. 


MANUFACTURE  OF  TIME 

9.  Common  lime  is  made  by  the  calcination,  or  burning, 
in  kilns,  of  limestone  that  is  composed  of  pure  or  very  nearly 
pure  carbonate  of  lime,  CaC03.  The  burning  is  made  at  a 
temperature  of  from  1,400°  to  2,000°  F.,  which  drives  off  part 
of  the  constituents  in  the  form  of  carbon  dioxide,  C02, 
leaving  a  product  composed  of  practically  pure  oxide  of 
calcium,  CaO.  The  lime  is  prepared  for  use  by  the  addition 
of  water,  which  converts  it  into  calcium  hydrate,  Ca(OH)2. 
This  process  is  called  slaking. 

If  lime  is  underburned,  it  will  not  slake  evenly,  and  hard 
pieces  will  be  left  that  will  not  disintegrate  when  water  is 
first  added.  If  such  lime  is  used  in  any  work,  the  unslaked 
particles  will  disintegrate  after  being  incorporated  in  the 
building,  resulting  in  swelling,  or  blowing ,  and  thus  injuring 
the  appearance  and  weakening  the  strength  of  the  work. 
Blowing  is  particularly  disastrous  in  plastering  work,  as  it 
spoils  the  smooth  surface  that  is  necessary. 

Overburned  lime  also  slakes  slowly  and  cannot  be  employed 
to  advantage. 

10.  Hydrated  lime  is  prepared  by  crushing  and  grinding 
lump  lime  to  a  fine  powder  and  then  hydrating,  or  slaking, 
it  by  sprinkling  water  over  it.  The  operation  is  performed 
in  a  shallow  pan  provided  with  plows,  which  keep  turning  the 
lime  over  so  as  to  insure  a  thorough  and  even  wetting.  The 
heat  drives  off  the  surplus  water,  leaving  the  hydrated  lime 
as  a  fine  powder. 

Hydrated  lime  is  considered  better  for  use  with  Portland 
cement  than  ordinary  slaked  lime,  both  because  it  is  more 


§29 


SANDS  AND  CEMENTS 


5 


easily  handled  and  measured  and  because  it  is  thoroughly 
slaked.  The  latter  property  prevents  the  mortar  from 
disintegrating. 


PROPERTIES  OF  TIME 

11.  Lime  is  slaked  by  spreading  it  on  a  suitable  bed  and 
then  moistening  it  with  water.  This  moistening  gives  rise 
to  various  phenomena.  The  lime  almost  immediately  cracks, 
swells,  and  falls  into  a  fine  white  powder,  with  a  hissing  sound 
and  the  evolution  of  heat  and  steam.  The  same  process  takes 
place  slowly  by  the  absorption  of  moisture  from  the  atmos¬ 
phere.  The  lime  falls  into  powder  with  increase  of  volume, 
but  without  perceptible  heating.  Lime  slaked  in  the  latter 
way  is  said  to  be  air-slaked.  It  is  deficient  in  setting  proper¬ 
ties,  however,  and  should  not  be  employed  for  structural 
purposes. 

The  quantity  of  water  required  for  slaking  is  about  one- 
third  the  volume  of  the  lime.  The  entire  quantity  should  be 
applied  by  sprinkling  at  one  operation.  The  addition  of  cold 
water  after  the  slaking  has  commenced  lowers  the  temper¬ 
ature  of  the  mixture  and  renders  the  lime  granular  and  lumpy. 
An  excess  of  water  reduces  the  binding  qualities. 

12.  The  quality  of  common  lime  is  indicated  by  the 
readiness  with  which  the  lumps  fall  to  powder  during  slaking. 
Good  lime  should  be  free  from  unslaked  lumps,  the  presence 
of  which  indicates  that  the  limestone  was  not  pure  or  that 
the  process  of  calcination  was  imperfect. 

In  order  to  obtain  complete  reduction,  lime  should  be 
slaked  several  days  before  it  is  to  be  used.  The  resulting 
paste  may  be  kept  indefinitely,  provided  it  is  protected  from 
the  elements  by  being  covered  with  the  sand  with  which  it 
will  subsequently  be  mixed  to  make  mortar. 

13.  Meager  limes  act  similarly  to  fat  limes,  except  that 
they  are  less  energetic.  Lime  containing  more  than  5  or 
10  per  cent,  of  magnesia  produces  a  mortar  of  greater  strength, 
but  such  limes  are  slower  slaking  and  less  smooth,  and  for 
these  reasons  they  are  not  liked  so  well  by  builders. 


6 


SANDS  AND  CEMENTS 


§29 


14.  Lime  hardens  by  reason  of  the  gradual  absorption 
from  the  air  of  carbon  dioxide,  C02,  which  slowly  changes  the 
lime  from  the  form  of  calcium  hydrate,  Ca(OH)2 ,  to  calcium 
carbonate,  CaC03,  so  that  the  final  result  is  to  restore  the 
material  to  its  original  condition  prior  to  burning,  hardened 
lime  mortar  being  practically  limestone  containing  sand.  To 
secure  this  result,  however,  all  parts  of  the  mortar  must  be 
readily  accessible  to  dry  air.  If  placed  in  damp  situations 
or  under  water,  or  if  excluded  from  contact  with  the  air, 
lime  mortars  will  not  harden.  Even  in  the  interior  of  thin 
building  walls  of  brick  laid  in  lime  mortar,  the  lime  will  be 
soft,  crumbly,  and  sometimes  even  plastic  after  several  years, 
although  the  edges  of  the  mortar,  where  exposed,  are  per¬ 
fectly  hard.  It  is  chiefly  for  this  reason  that  lime  mortars 
are  not  employed  in  important  work. 


CEMENTS 


CLASSIFICATION  OF  CEMENTS 

15.  Cement  may  be  divided  into  four  general  classes: 
Portland ,  natural ,  puzzolan  (also  called  pozzuolana) .  and  mixed. 
The  relative  importance  of  each  cement  is  indicated  by  the 
order  in  which  it  is  named. 

16.  Portland  cement  may  be  defined  as  the  product 
resulting  from  the  process  of  grinding  an  intimate  mixture  of 
calcareous  (containing  lime)  and  argillaceous  (containing  clay) 
materials,  calcining  (heating)  the  mixture  until  it  starts  to  fuse, 
or  melt,  and  grinding  the  resulting  clinker  to  a  fine  powder. 
It  must  contain  not  less  than  1.7  times  as  much  lime  by 
weight  as  it  does  of  those  materials  which  give  the  lime  its 
hydraulic  properties,  and  must  contain  no  materials  added 
after  calcination,  except  small  quantities  of  certain  substances 
used  to  regulate  the  activity  or  the  time  of  setting. 

17.  Natural  cement  is  the  product  resulting  from  the 
burning  and  subsequent  pulverization  of  an  argillaceous  lime- 


§29 


SANDS  AND  CEMENTS 


7 


stone  or  other  suitable  rock  in  its  natural  condition,  the  heat 
of  burning  being  insufficient  to  cause  the  material  to  start 
to  melt. 

18.  Puzzolan  cement  is  a  material  resulting  from 
grinding  together,  without  subsequent  calcination,  an  intimate 
mixture  of  slaked  lime  and  a  puzzolanic  substance,  such  as 
blast-furnace  slag  or  volcanic  scoria. 

19.  Mixed  cements  cover  a  wide  range  of  products 
obtained  by  mixing,  or  blending,  the  foregoing  cements  with 
each  other  or  with  other  inert  substances.  Sand  cements , 
improved  cements ,  and  many  second-grade  cements  belong 
to  this  class.  Mixed  cements,  however,  are  of  comparatively 
little  importance,  since  they  are  rarely  encountered  in  the 
market. 


CEMENT  MANUFACTURE 

20,  Portland  Cement. — Portland  cement  is  made 
from  a  great  variety  of  materials,  the  most  common  combi¬ 
nations  of  ingredients  used  in  the  United  States  being  argilla¬ 
ceous  limestone  and  pure  limestone;  limestone  and  clay; 
marl  or  chalk  and  clay;  and  blast-furnace  slag  and  limestone. 
After  the  separate  ingredients  have  been  subjected  to  chemical 
analysis  and  their  composition  determined,  they  are  mixed 
in  suitable  proportions  and  ground  together  to  an  extremely 
fine  powder.  The  powdered  mixture  is  then  burned  in  rotary 
kilns,  which  consist  of  long,  slowly  revolving,  horizontal 
cylinders.  The  mixture  is  fed  into  one  end  of  the  kiln  and 
passes  toward  the  other  end,  where  it  is  met  by  a  blast  of 
flame,  which  calcines  the  mixture  and  changes  it  into  a 
clinker  before  it  passes  out  of  the  kiln.  The  temperature  of 
burning  averages  about  2,700°  F. 

The  burned  clinker  is  in  the  form  of  irregular  round  balls 
about  the  size  of  a  walnut,  and  after  cooling,  this  clinker  is 
ground  to  a  fine  powder.  Cement  made  in  this  manner  is 
usually  extremely  quick-setting  and  hardens  so  rapidly  that 
it  cannot  be  properly  handled.  To  overcome  this  condition, 


8 


SANDS  AND  CEMENTS 


§29 


a  small  quantity  of  calcium  sulphate  (plaster  of  Paris,  or 
gypsum)  is  mixed  with  the  finished  cement,  the  result  of  this 
addition  being  to  retard  its  activity,  or  rate  of  setting. 

Cement  made  by  this  process  from  blast-furnace  slag  and 
limestone  is  considered  to  be  a  true  Portland  cement.  If, 
however,  the  material  is  not  burned,  the  product  is  classed 
as  puzzolan. 

The  distinguishing  characteristics  of  the  manufacture  of 
Portland  cement  are  the  use  of  an  artificial  mixture,  the 
grinding  before  calcination,  and  the  calcination  to  incipient 
fusion. 

21.  Natural  Cement. — Natural  cement  is  made  by  the 
direct  burning  of  an  argillaceous  limestone,  without  the 
admixture  of  any  other  substances.  The  rock  is  not  ground 
before  burning,  but  is  fed  into  the  kilns  just  as  it  comes  from 
the  quarry.  The  kilns  consist  of  vertical,  stationary  cylinders, 
into  the  top  of  which  the  cement  rock  and  the  fuel  are  placed 
in  alternate  layers,  the  burned  cement  being  drawn  finally 
from  the  bottom.  After  pulverization,  the  material  is  ready 
for  the  market. 

The  process  is  characterized  by  the  use  of  a  single  variety 
of  material  in  its  natural  condition,  the  lack  of  grinding  before 
burning,  and  the  lower  heat,  about  1,500°  F.,  employed,  as 
compared  with  that  required  for  Portland  cement. 

22.  A  large  portion  of  the  natural  cement  made  in  the 
United  States  is  produced  in  the  Rosendale  district  of  New 
York  State,  and  in  the  Louisville  district  lying  in  Indiana 
and  Kentucky.  Natural  cement,  accordingly,  is  often 
referred  to  as  Rosendale  or  Louisville  cement,  but  this 
usage  is  incorrect,  unless  applied  merely  to  the  cements  pro¬ 
duced  in  those  districts.  Certain  natural  cements  made  in 
Europe  are  known  as  Roman  cements.  Natural  cement  is 
cheaper  than  Portland,  but  it  is  neither  so  reliable  nor  does 
it  possess  such  good  qualities. 

23.  Puzzolan  Cements. — The  only  variety  of  puzzo¬ 
lan  cement  employed  at  all  extensively  in  American  practice 


§29 


SANDS  AND  CEMENTS 


9 


is  slag:  cement.  This  cement  is  made  by  grinding  together 
a  mixture  of  blast-furnace  slag  and  slaked  lime.  The  slag 
used  for  this  purpose  is  granulated,  or  quenched,  in  water  as 
soon  as  it  leaves  the  furnace,  which  operation  drives  off  most 
of  the  dangerous  sulphides  and  renders  the  slag  puzzolanic. 
Slag  cooled  slowly  in  air  is  not  suitable  for  cement.  The  lime 
employed  is  a  fat  quicklime  that  is  thoroughly  slaked  and 
then  dried.  A  small  quantity  of  caustic  soda  is  also  generally 
added  to  the  mixture,  so  as  to  hasten  the  otherwise  rather 
slow  time  of  setting.  The  distinguishing  feature  of  the  process 
is  the  absence  of  any  burning. 

The  orginal  puzzolan  cement  was  made  by  mixing  lime 
with  scoria  that  was  obtained  at  the  foot  of  Mount  Vesuvius 
in  Italy.  It  was  the  latter  material  that  was  used  by  the 
Romans  in  their  famous  constructions.  A  volcanic  material 
called  trass ,  found  in  Germany  and  Holland,  and  a  sand 
known  as  Arenes,  found  in  France,  are  other  examples  of 
puzzolanic  substances. 

24.  Mixed  Cements. — A  mixed  cement  known  as  silica, 
or  sand,  cement  is  made  by  grinding  together  Portland 
cement  and  sand,  usually  in  equal  parts.  The  sand  is  merely 

-  i 

an  adulterant,  but  the  extra-hne  grinding  that  the  cement 
receives  increases  its  sand-carrying  capacity,  so  that  its 
resulting  strength  is  but  little  less  than  that  of  Portland 
cement. 


25.  Improved  cement  is  made  from  a  mixture  of 
Portland  and  natural  cements.  The  mixture  usually  contains 
from  10  to  25  per  cent,  of  the  former  and  from  75  to  90  per 
cent,  of  the  latter.  The  combination  possesses  many  of  the 
good  features  of  both  materials,  and  increases  the  value  of 
natural  cement  in  a  proportion  greater  than  the  increased 
expense. 

26.  Other  varieties  of  mixed  cements  are  often  sold  as 
second-grade  Portlands ,  and  consist  of  cement  mixed  with  raw 
rock,  cinders,  sand,  or  inferior  clinker.  The  use  of  such 
cements  should  not  be  tolerated  in  important  structures. 


10 


SANDS  AND  CEMENTS 


§29 


PROPERTIES  OF  CEMENTS 

27.  The  hydraulic  cements  differ  from  the  limes  in  that 
they  do  not  slake  after  calcination,  and  that  they  set,  or 
harden,  under  water.  They  can  be  formed  into  a  paste  with 
water  without  any  sensible  increase  in  volume  and  with  little, 
if  any.  disengagement  of  heat.  They  do  not  shrink  appreci¬ 
ably  in  hardening,  so  that  the  sand  and  broken  stone  with 
which  they  are  mixed  are  employed  merely  through  motives 
of  economy  and  not,  as  with  limes,  of  necessity. 

28.  Composition. — Hydraulic  cements  are  composed 
essentially  of  silica,  alumina,  and  lime,  and  also  contain,  in 
smaller  quantities,  iron  oxide,  magnesia,  and  sulphuric  acid. 
In  Portland  cement,  the  active  ingredients  are  certain  silicates 
and  aluminates  of  lime.  The  iron  oxide  acts  similarly  to  the 
alumina,  but  is  usually  present  in  much  smaller  quantity. 
The  gray  color  of  cement  is  due  to  the  presence  of  this  iron, 
since  the  silicates  and  aluminates  of  lime  are  white.  Magnesia 
acts  as  an  adulterant,  and  if  present  in  excess  of  4  or  5  per 
cent.,  may  impart  injurious  properties  to  the  material,  espe¬ 
cially  if  it  is  used  in  sea-water.  The  presence  of  sulphuric 
acid  is  principally  due  to  the  addition  of  calcium  sulphate, 
which  is  employed  to  control  the  time  of  setting.  Like 
magnesia,  sulphuric  acid  is  injurious  if  present  in  excess. 

29.  When  water  is  added  to  Portland  cement,  the  silicates 
and  aluminates  of  lime  are  decomposed  and  go  partly  into 
solution,  from  which  calcium  hydrate  is  precipitated  and 
crystallized  in  the  form  of  long,  needle-like,  interlocking 
crystals.  The  strength  of  cement  is  due  to  the  formation  of 
these  crystals,  and  the  continued  process  of  this  crystallization 
gives  the  cement  its  property  of  increasing  in  hardness  and 
strength.  The  setting  of  cement,  then,  is  due  to  the  solution 
of  the  aluminates  of  lime,  while  the  slower  decomposition 
and  crystallization  from  the  silicates  gives  the  cement  its 
strength,  which  increases  with  age.  The  precise  chemical 
reactions  that  take  place  in  the  setting  and  hardening  of 
hydraulic  cements  are  still,  however,  disputed  questions. 


§29 


SANDS  AND  CEMENTS 


11 


30.  Color. — The  color  of  the  different  grades  of  cement 
is  variable,  but  in  certain  cases  it  is  distinctive.  Portland 
cement  is  a  dark-bluish  or  greenish  gray;  if  it  is  a  light  yellow, 
it  may  indicate  underburning.  Natural  cement  ranges  in 
color  from  a  light  straw,  through  the  grays,  to  a  chocolate 
brown.  Slag  cement  is  gray  with  usually  a  tinge  of  lilac. 
In  general,  however,  the  color  of  cement  is  no  criterion  of  its 
quality,  except  when  a  certain  brand  shows  a  variation  in 
color,  thus  indicating  a  lack  of  uniformity  in  the  raw  materials 
or  in  the  process  of  manufacture. 

31.  Wei glit. — Cement  is  packed  either  in  wooden  barrels 
or  in  cloth  or  paper  bags,  the  latter  being  the  form  of  package 
most  commonly  employed.  A  barrel  of  Portland  or  of  slag 
cement  contains  the  equivalent  of  four  bags,  while  but  three 
bags  of  natural  cement  equals  a  barrel.  The  average  weights 
of  the  various  cements  are  given  in  Table  I. 

TABLE  I 

AVERAGE  WEIGHTS  OF  HYDRAULIC  CEMENTS 


Kind  of  Cement 

Net  Weight 
of  Bag 

Net  Weight 
of  Barrel 

Weight  per  Cubic  Foot 
Pounds 

Pounds 

Pounds 

Packed 

Loose 

Portland . 

94 

376 

100-120 

70-90 

Natural  . 

94 

282 

75-95 

45-65 

Slag . 

82I 

330 

80—100 

55-75 

In  proportioning  mortar  or  concrete  by  volume,  the  com¬ 
mon  assumption  is  that  a  bag  of  Portland  cement  occupies 
.9  cubic  toot. 

32.  Physical  Properties.  —  Hydraulic  cements  are 
characterized  by  the  properties  of  specific  gravity,  time  of 
setting,  fineness,  strength,  soundness,  and  composition.  A 
discussion  of  these  properties,  the  methods  of  testing  employed 
in  determining  them,  and  the  specifications  used  for  cements 


12 


SANDS  AND  CEMENTS 


§29 


that  are  based  on  these  properties  will  be  given  in  another 
Section. 


33.  Distinguishing  Characteristics.  —  Portland 

cement  may  be  distinguished  by  its  dark  color,  heavy  weight, 
slow  rate  of  setting,  and  greater  strength.  Natural  cement 
is  characterized  by  lighter  color,  lighter  weight,  quicker  set, 
and  lower  strength.  Slag  cement  is  somewhat  similar  to 
Portland,  but  may  be  distinguished  from  it  by  its  lilac-bluish 
color,  by  its  lighter  weight,  and  by  the  greater  fineness  to 
which  it  is  ground. 

34.  Adaptability.  —  Portland  cement  is  adaptable  to 
any  class  of  mortar  or  concrete  construction,  and  is  unques¬ 
tionably  the  best  material  for  all  such  purposes.  Natural  and 
slag  cements,  however,  are  cheaper,  and  under  certain  con¬ 
ditions,  may  be  substituted  for  the  more  expensive  Portland 
cement.  All  heavy  construction,  especially  if  exposed,  all 
reinforced-concrete  work,  sidewalks,  concrete  blocks,  founda¬ 
tions  of  buildings,  piers,  walls,  abutments,  etc.,  should  be 
made  with  Portland  cement.  In  second-class  work,  such  as 
is  used  in  rubble  masonry,  brick  sewers,  unimportant  wx>rk 
in  damp  or  wet  situations,  or  in  heavy  work  in  which  the 
working  loads  will  not  be  applied  until  long  after  completion, 
natural  cement  may  be  employed  to  advantage.  Slag  cement 
is  best  adapted  to  heavy  foundation  work  that  is  immersed 
in  water  or  at  least  continually  damp.  This  kind  of  cement 
should  never  be  exposed  directly  to  dry  air,  nor  should  it  be 
subjected  either  to  attrition  or  impact. 


MISCELLANEOUS  CEMENTING  MATERIALS 

35.  Plaster  is  probably  the  most  important  of  the 
miscellaneous  cementing  materials.  It  is  made  by  burning 
a  sulphate  of  lime  known  as  gypsum.  By  this  treatment 
most  of  the  water  is  drawn  off  and  the  material  is  rendered 
cementitious.  The  most  common  varieties  of  plaster  are 
known  as  plaster  of  Paris  or  stucco ,  flooring  plaster ,  and  wall 


§29 


SANDS  AND  CEMENTS 


13 


plaster  (prepared  by  mixing  with  hair).  Keene's  cement  and 
Parian  cement  are  varieties  of  plaster  used  for  hard  finishes 
in  buildings. 

36.  Since  the  common  hydraulic  cements  will  often 
destroy  the  appearance  of  the  stone  at  the  joints,  the  non- 
staining:  cements  have  been  devised  for  use  in  exterior  walls 
of  buildings  made  of  cut  stone.  These  cements  are  either  of 
the  Portland  type  from  which  the  iron  has  been  eliminated 
or  of  the  puzzolan  type.  Several  imported  and  one  or  two 
American  cements  of  this  kind  are  to  be  found  on  the  market. 

37.  For  waterproofing  purposes,  cements  have  been 
devised  that,  when  hardened,  tend  to  resist  the  action  of 
water  and  keep  the  interior  of  the  construction  dry. 

38.  Bituminous  cements  and  coal-tar  cements 
are  materials  used  in  laying  cellar  floors,  or  for  waterproofing 
walls,  arches,  tunnels,  etc.  These  materials  are  the  only 
ones  that  combine  elasticity  with  the  property  to  resist  water. 

39.  Numerous  cementing  materials  are  made  for  other 
special  purposes,  but  their  use  is  comparatively  limited  and 
hence  will  not  be  discussed  in  this  Section. 


14 


SANDS  AND  CEMENTS 


§29 


SAND  AND  ITS  MIXTURES 


SAND 


INTRODUCTION 

40.  Sand  is  an  aggregation  of  loose,  incoherent  grains 
of  crystalline  structure,  derived  from  the  disintegration  of 
rocks.  It  is  called  silicious,  argillaceous,  or  calcareous, 
according  to  the  character  of  the  rock  from  which  it  is  derived. 
Sand  is  obtained  from  the  seashore,  from  the  banks  and  beds 
of  rivers,  and  from  land  deposits.  The  first  class,  called  sea 
sand,  contains  alkaline  salts  that  attract  and  retain  moisture 
and  cause  efflorescence  in  brick  masonry.  This  efflorescence 
is  not  at  first  apparent  but  becomes  more  marked  as  time 
goes  on.  It  can  be  removed  temporarily  at  least  by  washing 
the  stonework  in  very  dilute  hydrochloric  acid.  The  second, 
termed  river  sand,  is  generally  composed  of  rounded 
particles,  and  may  or  may  not  contain  clay  or  other  impurities. 
The  third,  called  pit  sand,  is  usually  composed  of  grains 
that  are  more  angular;  it  often  contains  clay  and  organic 
matter.  When  washed  and  screened,  it  is  a  good  sand  for 
general  purposes. 

41.  Uses  of  Sand. — The  principal  reasons  for  using 
sand  in  making  mortar  are  that  it  prevents  excessive  shrinkage 
and  reduces  the  quantity  of  lime  or  cement  required.  Lime 
adheres  better  to  the  particles  of  sand  than  it  does  to  its  own 
particles;  hence,  it  is  considered  that  sand  adds  strength  to 
lime  mortar.  On  cement  mortar,  on  the  contrary,  sand  has 
a  weakening  effect.  Sand  is  also  used  as  a  cushion  to  dis¬ 
tribute  the  pressure  of  structures  over  soft  soils,  as  in  a 
foundation  and  joint  filling  for  pavements,  and  for  plastering. 


§  29 


SANDS  AND  CEMENTS 


15 


TESTING  OF  SAND 

42.  The  quality  of  sand  intended  for  use  in  mortar  is 
ascertained  by  determinations  of  its  weight,  specific  gravity, 
percentage  of  voids,  character  of  grain,  fineness,  purity,  and 
by  strength  tests  of  the  actual  mortar.  For  mortars  and 
concretes  of  cement,  the  character  of  the  sand  employed  is 
most  important,  since  it  vitally  affects  the  strength,  density, 
and  permanency  of  the  finished  structure. 

43.  Weight. — The  weight  of  sand  is  determined  by 
merely  filling  a  cubic-foot  measure  with  dried  sand  and 
obtaining  its  weight.  Dry  sand  weighs  from  80  to  120 
pounds  per  cubic  foot;  moist  sand,  however,  occupies  more 
space  and  weighs  less  per  cubic  foot.  The  weight  of  sand  is 
more  or  less  dependent  on  its  specific  gravity  and  on  the 
size  and  shape  of  the  sand  grains,  but,  other  things  being 
equal,  the  heaviest  sand  makes  the  best  mortar. 

44.  Specific  Gravity. — The  specific  gravity  of  sand  is 
found  by  a  method  similar  to  that  used  for  finding  the  specific 
gravity  of  cement,  and  will  be  described  in  another  Section ; 
it  ranges  from  2.55  to  2.80.  For  all  practical  purposes,  the 
specific  gravity  may  be  assumed  to  be  2.65  with  little  danger 
of  error. 

45.  Percentage  of  Voids. — By  percentage  of  voids 
is  meant  the  amount  of  air  space  in  the  sand.  Struc¬ 
turally,  it  is  one  of  the  most  important  properties  of  sand. 
The  greater  these  voids,  the  more  cement  paste  will  be 
required  to  fill  them  in  order  to  give  a  dense  mortar;  or, 
conversely,  with  a  given  proportion  of  cement  and  sand,  the 
sand  that  has  the  smallest  voids  will  produce  the  strongest, 
the  densest,  and  the  most  impervious  mortar. 

The  percentage  of  voids  may  be  determined  by  observing 
the  quantity  of  water  that  can  be  introduced  into  a  vessel 
filled  with  sand,  but  it  is  best  computed  from  the  specific 
gravity  and  the  weight  per  cubic  foot  of  the  sand  to  be  tested. 
The  weight  per  cubic  foot  of  sand  containing  no  voids  at  all 


16 


SANDS  AND  CEMENTS 


§29 


is  evidently  equal  to  the  product  of  its  specific  gravity  times 
62.5,  or  the  weight  of  water  per  cubic  foot.  Therefore,  it 
follows  that 

r  •  100  X  weight  per  cubic  foot 

percentage  of  voids  =  100 - ; - : - 

62.5  X  specific  gravity 

Example. — What  is  the  percentage  of  voids  in  a  sand  having  a 
specific  gravity  of  2.65  and  weighing  105  pounds  per  cubic  foot? 

Solution. — Substituting  in  the  formula,  the  percentage  of  voids  is 

10°-6^H=100  -  63'4-36'6-  AnS' 

The  percentage  of  voids  is  dependent  principally  on  the 
size  and  shape  of  the  sand  grains  and  the  gradation  of  its 
fineness,  and  hence  will  vary  from  25  to  50  per  cent.  Sand 
containing  over  45  per  cent,  of  voids  should  not  be  used  to 
make  mortars. 

46.  Sliape  of  Sand  Grains. — The  shape  of  the  grains  of 
sand  is  of  chief  importance  in  the  influence  that  the  sand 
exerts  on  the  percentage  of  voids.  Obviously,  a  sand  with 
rounded  grains  will  compact  into  a  more  dense  mass  than 
one  whose  grains  are  angular  or  flat  like  particles  of  mica. 
Therefore,  the  more  nearly  the  grains  approach  the  spherical 
in  shape,  the  more  dense  and  strong  will  be  the  mortar. 
This  fact  must  be  carefully  remembered,  as  it  is  contrary 
to  the  common  opinion  on  the  subject. 

47.  Fineness. — The  fineness  of  sand  is  determined  by 
passing  a  dried  sample  through  a  series  of  sieves  having  10, 
20,  30,  40,  50,  74,  100,  and  200  meshes,  respectively,  to  the 
linear  inch.  The  result  of  this  test,  expressed  in  the  amount 
of  sand  passing  each  sieve,  is  known  as  the  granulometric 
composition  of  the  sand.  Material  that  does  not  pass  a 
|-inch  screen  is  not  considered  to  be  sand,  and  should  be 
separated  by  screening.  Sand  that  is  practically  all  retained 
on  a  No.  30  sieve  is  called  coarse,  while  80  or  90  per  cent,  of 
sand  known  as  fine  will  pass  through  this  sieve.  Fine  sand 
produces  a  weaker  mortar  than  coarse  sand,  but  a  mixture  of 
fine  and  coarse  sand  will  surpass  either  one. 


§29 


SANDS  AND  CEMENTS 


17 


48.  Purity. — The  purity,  or  cleanness,  of  sand  may  be 
roughly  ascertained  by  rubbing  it  between  the  fingers  and 
observing  how  much  dirt  remains.  To  determine  the  per¬ 
centage  of  the  impurities  more  accurately,  a  small  dried 
and  weighed  sample  is  placed  in  a  vessel  and  stirred  up  with 
water.  The  sand  is  allowed  to  settle,  the  dirty  water  poured 
off,  and  the  process  repeated  until  the  water  pours  off  clear. 
The  sand  is  then  dried  and  weighed.  The  loss  in  wTeight 
gives  the  quantity  of  impurities  contained  in  the  sand. 
The  presence  of  dirt,  organic  loam,  mica,  etc.  is  decidedly 
injurious  and  tends  to  weaken  the  resulting  mortar.  Clay  or 
fine  mineral  matter  in  small  proportions  may  actually  result 
in  increased  strength,  but  excessive  quantities  of  these  mate¬ 
rials  may  be  a  possible  source  of  weakness.  The  best  modern 
practice  limits  the  quantity  of  impurities  found  by  this 
washing  test  to  5  per  cent. 

49.  Strength  of  Sand  Mortar. — It  is  also  advisable, 
prior  to  the  selection  of  a  sand,  to  determine  what  its  strength 
will  be  when  made  into  mortar.  Sands  that  appear  excellent 
are  sometimes  incorporated  into  work,  with  the  result  that 
a  weak  and  soft  mortar  is  obtained,  thereby  causing  the 
loss  of  considerable  time  and  money.  Proper  care  in  the 
selection  of  sand,  even  if  costly,  will  generally  prove  to  be 
true  economy,  especially  if  the  sand  is  to  be  used  in  important 
structures. 


PREPARATION  OF  SAND 

50.  Sand  is  prepared  for  use  by  (1)  screening  to  remove 
the  pebbles  and  coarser  grains,  the  fineness  of  the  meshes 
of  the  screen  depending  on  the  kind  of  work  in  which  the  sand 
is  to  be  used ;  (2)  washing,  to  remove  salt,  clay,  and  other 
foreign  matter;  and  (3)  drying,  if  necessary.  When  dry 
sand  is  required,  it  is  obtained  by  evaporating  the  moisture 
either  in  a  machine,  called  a  sand  dryer ,  or  in  large,  shallow, 
iron  pans  supported  on  stones,  with  a  wood  fire  placed 
underneath. 


18 


SANDS  AND  CEMENTS 


§29 


MORTARS 


PROPORTIONS  OF  INGREDIENTS 

51.  Mortars  for  structural  purposes  are  composed  of 
lime  or  cement  and  sand  mixed  to  the  proper  consistency 
with  water.  The  proportions  of  the  ingredients  depend  on 
the  character  of  the  work  in  which  the  mortar  is  to  be  used. 
The  quality  of  the  mortar  depends  on  the  quality  of  its  con¬ 
stituents,  the  proportions  in  which  they  are  combined,  and 
the  methods  by  which  they  are  mixed  and  used. 

In  proportioning  mortar,  it  is  customary  to  designate  the 
quantities  of  the  separate  ingredients  by  a  ratio,  such  as 
1-1,  1-2,  1-3,  etc.  Thus,  1-1  signifies  that  the  mortar  is 
composed  of  1  part  of  lime  or  cement  to  1  part  of  sand; 
1-2,  that  1  part  of  lime  or  cement  is  used  to  2  parts  of  sand; 
etc.  These  measurements  are  usually  made  by  volume 
instead  of  by.  weight.  The  first  number  of  the  ratio  always 
indicates  the  quantity  of  lime  or  cement,  which  for  con¬ 
venience,  is  taken  at  unity  of  volume. 


LIME  MORTARS 

52.  Ingredients. — Sand  is  added  to  lime  or  cement  to 
increase  its  bulk  and  thus  cheapen  the  material.  In  lime 
mortar,  however,  besides  effecting  an  economy,  the  presence 
of  sand  is  necessary  to  prevent  the  shrinkage  that  would 
otherwise  occur  during  the  hardening  of  the  paste. 

When  a  mortar  is  made  of  lime  and  sand,  enough  lime 
should  be  present  to  just  cover  completely  each  grain  of  sand. 
An  excess  of  lime  over  this  quantity  causes  the  mortar  to 
shrink  excessively  on  drying,  while  a  deficiency  of  lime 
produces  a  weak  and  crumbly  mortar.  The  correct  quantity 
of  lime  depends  on  the  character  of  the  ingredients,  the 
method  of  treatment,  and,  to  some  extent,  on  the  judgment 
of  the  builder,  the  mixtures  employed  varying  from  1-21 
to  1-5.  Building  laws  in  many  municipalities  require  the 


SANDS  AND  CEMENTS 


19 


$  29 


use  of  a  1-3  mixture,  and  for  most  materials  this  proportion 
will  be  found  satisfactory,  although  for  rich,  fat  limes  a 
l-3£  or  a  1-4  mixture  is  sometimes  preferable. 

53.  Mixing. — In  mixing  lime  mortar,  a  bed  of  sand  is 
made  in  a  mortar  box,  and  the  lime  distributed  as  evenly  as 
possible  over  it,  first  measuring  both  the  lime  and  the  sand 
in  order  that  the  proportions  specified  may  be  obtained. 
The  lime  is  then  slaked  by  pouring  on  water,  after  which 
it  should  be  covered  with  a  layer  of  sand,  or,  preferably, 
a  tarpaulin,  to  retain  the  vapor  given  off  while  the  lime  is 
undergoing  the  chemical  reaction  of  slaking.  Additional 
sand  is  then  used,  if  necessary,  until  the  mortar  attains  the 
proper  proportions. 

Care  should  be  taken  to  add  just  the  proper  quantity  of 
water  to  slake  the  lime  completely  to  a  paste.  If  too  much 
water  is  used,  the  mortar  will  never  attain  its  proper  strength, 
while  if  too  little  is  used  at  first,  and  more  is  added  during 
the  process  of  slaking,  the  lime  will  have  a  tendency  to  chill, 
thereby  injuring  its  setting  and  hardening  properties.  Rather 
than  make  up  small  batches,  it  is  considered  better  practice 
to  make  lime  mortar  in  large  quantities  and  to  keep  it  standing 
in  bulk  so  that  it  can  be  used  as  needed. 

54.  Use  of  Dime  Mortar. — Lime  mortar  is  employed 
chiefly  for  brickwork  of  the  second  class,  and  its  use  is  contin¬ 
ually  decreasing  as  that  of  cement  increases.  It  is  absolutely 
unsuitable  for  any  important  construction,  because  it  possesses 
neither  strength  nor  the  property  of  resisting  water.  It 
cannot  be  used  in  damp  or  wet  situations,  nor  should  it  ever 
be  laid  in  cold  weather,  as  it  is  very  susceptible  to  the  action 
of  frost,  being  much  injured  thereby.  Moreover,  since  it 
hardens  by  the  action  of  dry  air,  only  the  exterior  of  lime 
mortar  ever  becomes  fully  hardened,  so  that  anything  like  a 
concrete  with  lime  as  a  matrix  is  impossible.  However, 
for  second-class  brickwork,  such  as  is  commonly  used  in  the 
walls  of  smaller  buildings,  lime  mortars  are  economical  and 
sufficiently  good. 


20 


SANDS  AND  CEMENTS 


§29 


55.  Strength  of  Dime  Mortars. — The  strength  of  lime 
mortars  is  extremely  variable,  depending  on  the  ingredients 
themselves  and  on  their  treatment,  environment,  etc.  More¬ 
over,  it  is  unsafe  to  figure  a  lime-mortar  joint  as  possessing 
much  strength,  since  only  a  part  of  the  joint  is  hardened 
and  capable  of  developing  any  strength  at  all.  The  tensile 
strength  of  thoroughly  hardened  1-3  lime  mortars  averages 
from  40  to  70  pounds  per  square  inch,  and  the  compressive 
strength  from  150  to  300  pounds. 


CEMENT  MORTARS 

56.  Ingredients. — Cement  mortars  consist  of  cement, 
sand,  and  water,  and  the  character  and  proportions  of  these 
ingredients  vitally  affect  the  properties  of  the  resulting  prod¬ 
uct.  As  has  been  stated,  the  cement  for  all  structures 
of  importance  should  be  Portland,  although  natural  and 
slag  cements  may  occasionally  be  employed  to  advantage 
where  the  conditions  permit. 

57.  The  sand  for  all  mortars  should  be  clean,  of  suitable 
size  and  granulometric  composition.  For  structures  designed 
to  withstand  heavy  unit  stresses,  or  for  those  intended 
to  resist  either  the  penetration  of  moisture  or  the  actual 
pressure  of  water,  the  selection  of  the  sand  should  be  most 
carefully  made.  Generally,  it  is  not  advisable  to  use  a  sand 
containing  over  5  per  cent,  of  loam  by  the  washing  test, 
nor  one  that  soils  the  fingers  when  it  is  rubbed  between  them. 
These  points  should  be  especially  considered  when  the  sand 
is  to  be  used  for  mortars  intended  for  facing,  pointing,  or 
waterproofing.  Moreover,  for  most  classes  of  work,  the 
preference  should  usually  be  given  to  a  rather  coarse  sand, 
although  sand  containing  all  sizes  of  grains,  from  coarse  to 
fine,  more  nearly  approaches  the  ideal  in  producing  the 
densest  and  strongest  mortar.  Very  fine  sand,  such  as  is 
found  on  the  seashore,  should  not  be  employed  in  mortar 
unless  it  is  intended  simply  for  pointing  or  for  grouting. 


§29 


SANDS  AND  CEMENTS 


21 


A  simple  method  of  determining  the  best  sand  for  cement 
mortar  is  to  prepare  mixtures  of  the  cement,  sand,  and  water, 
using  the  same  quantities  in  each  case,  and  then  to  place 
each  mixture  in  a  measure;  that  mixture  giving  the  least 
volume  of  mortar  may  be  considered  to  contain  the  most 
desirable  sand  for  use. 

Limestone  screenings,  brick  dust,  crushed  cinders,  etc., 
are  sometimes  substituted  for  sand  in  making  mortars,  and, 
if  care  is  taken  in  their  selection,  they  may  prove  economical 
and  entirely  suitable  for  the  purpose. 

58.  The  water  used  in  mixing  cement  mortar  should 

i 

be  clean,  fresh,  and  free  from  dirt  or  vegetable  matter.  Water 
containing  even  small  quantities  of  acid  may  seriously 
injure  the  mortar.  The  presence  of  oil  will  result  in  slow 
setting  and  decreased  strength.  Salt  water  may  be  used  if 
necessary,  but  it  also  retards  the  setting,  and  decreases  the 
strength. 

59.  Proportion  of  Ingredients. — The  theory  of  the 
composition  of  a  correctly  proportioned  mortar  is  that  the 
cement  paste  will  just  a  little  more  than  fill  all  the  voids 
between  the  particles  of  sand,  thus  giving  an  absolutely  dense 
mortar  at  the  least  expense.  If  more  cement  is  used,  the 
cost  will  be  increased,  while  less  cement  will  result  in  a  weaker 
and  porous  mortar.  The  correct  proportion  of  cement  to 
sand,  therefore,  is  more  or  less  variable,  depending  on  the 
granulometric  composition  of  the  sand.  Since,  however, 
Portland-cement  paste  that  has  set  weighs  nearly  as  much 
as  sand,  and  since  the  average  sand  contains  about  30  to 
40  per  cent,  of  voids,  it  is  evident  that  1-3  mixtures  most 
nearly  approach  the  best  and  most  economical  proportion. 
This  mixture  is  in  fact  most  generally  employed  for  mortars 
used  in  buildings,  walls,  etc.  and  is  the  proportion  commonly 
specified  by  corporations  and  municipalities  for  such  work. 

60.  Mortars,  however,  are  made  in  proportions  varying 
from  1-1  to  1-8.  The  richer  mixtures  are  used  for  facing, 
pointing,  waterproofing,  granolithic  mixtures,  etc.,  the 


22 


SANDS  AND  CEMENTS 


§29 


1-2  mixture  being  usually  made  for  such  purposes.  The 
leaner  mixtures  are  used  for  rough  work,  filling,  backing,  etc., 
but  should  never  be  employed  where  either  much  strength 
or  much  density  is  desired.  Natural-cement  mortars  are 
commonly  made  1  part  of  sand  less  than  Portland-cement 
mortars  intended  for  the  same  purpose;  that  is,  where  a 
1-3  Portland-cement  mortar  would  be  used,  a  1-2  natural 
mortar  would  be  required,  although  natural-cement  mortars 
should  be  decreased  by  about  2  parts  of  sand  to  equal  the 
strength  of  Portland.  In  other  words,  a  1-4  Portland  mortar 
closely  equals  the  strength  of  a  1-2  natural  mortar.  Puzzolan 
cements  are  usually  proportioned  the  same  as -Portlands. 

61.  Cements  are  commonly  proportioned  by  volume, 
the  unit  volume  of  the  cement  barrel  being  assumed.  Various 
values  for  this  unit  volume  are  taken  by  different  authorities, 
but  the  general  practice  is  to  assume  that  the  Portland- 
cement  barrel  contains  3.6  cubic  feet,  and  that  the  bag  contains 
.9  cubic  foot.  If  a  1-3  mortar  is  desired,  a  box  having  a 
capacity  of  10.8  cubic  feet  is  filled  with  sand  and  mixed  with 
4  bags  or  1  barrel  of  cement.  A  box  3  feet  3^  inches  square 
and  1  foot  deep  will  have  a  capacity  of  very  nearly  10.8  cubic 
feet  and  besides  makes  a  convenient  size  of  box  for  actual 
work. 

62.  The  quantity  of  water  required  varies  with  the 
richness  of  the  mixture  and  the  character  of  the  ingredients, 
so  that  it  is  difficult,  if  not  impossible,  to  state  just  how 
much  should  be  used  at  all  times.  For  general  purposes, 
the  mortar  should  be  of  a  plastic  consistency — firm  enough 
to  stand  at  a  considerable  angle,  yet  soft  enough  to  work 
easily.  Wet  mortars  are  easiest  to  work  and  are,  as  a  rule, 
the  strongest  and  most  dense  when  hardened.  However,  they 
are  subject  to  greater  shrinkage,  are  slower  setting,  and  are 
more  easily  attacked  by  frost.  Dry  mortars,  on  the  other 
hand,  are  often  friable  and  porous.  The  consistency  of  the 
mortar,  therefore,  should  vary  with  the  materials  used  and 
with  the  conditions  to  be  met. 


§29 


SANDS  AND  CEMENTS 


23 


63.  In  Table  II  are  given  the  quantities  of  materials 
required  to  produce  1  cubic  yard  of  compacted  mortar.  The 
proportions  are  by  volume,  a  cement  barrel  being  assumed 
to  contain  3.6  cubic  feet.  Of  course,  the  quantity  of  mortar 
produced  from  any  mixture  of  materials  will  vary  with  the 
character  of  the  ingredients,  but  the  data  given  in  the  table 
will  serve  as  a  guide  for  the  quantities  required  under  average 
conditions. 

TABLE  II 


MATERIALS  REQUIRED  PER  CUBIC  YARD  OF  MORTAR 


Kind  of  Mixture 

Portland  Cement 
Barrels 

Loose  Sand 
Cubic  Yards 

I— I . 

4-95 

1-2 . 

3.28 

.88 

l~3 . 

2.42 

1. 01 

i-4 . 

1.99 

1.06 

i-5 . . . 

1.62 

1. 11 

i-6 . 

i-34 

i*i5 

. 

1. 18 

1.17 

i-8 . 

1.05 

1. 18 

Example. — How  much  cement  and  sand  will  be  required  to  obtain 
8.5  cubic  yards  of  1-3  Portland-cement  mortar? 


Solution. — According  to  Table  II,  1  cu.  yd.  of  a  1-3  Portland- 
cement  mortar  requires  2.42  bbl.  of  cement;  therefore,  8.5  cu.  yd. 
will  require  8.5X2.42  =  20.57  bbl.  of  cement.  Also,  since  1  cu.  yd. 
of  a  mixture  of  this  kind  requires  1.01  cu.  yd.  of  sand,  the  quantity 
of  sand  required  will  be  8.5X1.01  =  8.59  cu.  yd.  Ans. 

64.  Mixing:. — It  is  essential  in  making  cement  mortars 
to  secure  a  complete  and  uniform  mixture  of  the  separate 
ingredients.  This  kind  of  a  mixture  is  of  course  best  obtained 
by  means  of  mechanical  contrivances;  but  since  mechanical 
mixers  are  expensive  to  install  and  operate,  it  is  only  on 
extensive  works,  where  large  quantities  of  material  can  be 
used  in  a  short  time,  that  such  appliances  can  be  employed 
to  advantage. 


24 


SANDS  AND  CEMENTS 


§29 


65.  Mortar  that  is  to  be  mixed  by  hand  is  prepared  on  a 
platform  or  in  a  mortar  box.  The  sand  is  first  measured 
by  means  of  a  bottomless  barrel,  or,  better,  by  means  of  a 
low,  square,  bottomless  box  with  handles  on  the  sides  and  of 
such  a  size  that  it  will  give  the  correct  proportion  of  sand. 
After  filling  the  box,  the  sand  is  struck  off  level,  the  box 
lifted  up,  and  the  sand  spread  in  a  low,  flat  pile.  The  required 
number  of  bags  of  cement  are  then  emptied  on  the  sand  and 
spread  evenly  over  it.  The  pile  is  then  turned  over  and 
mixed  with  shovels,  working  through  it  not  less  than  four 
times.  After  this  operation,  the  dry  mixture  is  formed  into 
a  ring,  or  crater,  and  the  water  intended  to  be  used  is  poured 
into  the  center.  The  material  from  the  sides  of  the  basin 
is  then  shoveled  into  the  center  until  the  water  is  entirely 
absorbed,  after  which  the  pile  is  worked  again  with  shovels 
and  hoes  until  the  mixture  is  uniform  and  in  a  plastic  con¬ 
dition.  In  mixing,  the  mortar  should  be  completely  turned 
over  not  less  than  four  times  dry  and  from  four  to  six  times 
after  the  water  has  been  added. 

66.  Another  method  of  mixing,  where  a  mortar  box 
is  used,  is  to  gather  the  mixed  dry  materials  at  one  end  of 
the  box  and  pour  in  the  water  at  the  other  end,  drawing 
the  mixture  into  the  water  with  a  hoe  a  little  at  a  time, 
and  hoeing  until  a  plastic  consistency  is  obtained. 

67.  Good  results  can  be  secured  by  either  method, 
provided  sufficient  care  is  exercised.  If  a  batch  of  mortar  is 
once  made  too  wet,  it  cannot  be  brought  back  properly  to  a 
drier  consistency;  also,  an  excessively  wet  mortar  is  difficult 
to  work  and  is  often  productive  of  poor  results.  The  best 
plan,  therefore,  in  adding  the  water  is  to  pour  in  first  a  little 
less  than  is  required  and  then  make  up  the  deficiency  by 
means  of  a  watering  can  or  a  sprinkling  hose.  In  this  way, 
an  excess  of  water  is  guarded  against. 


§29 


SANDS  AND  CEMENTS 


25 


PROPERTIES  AND  USES  OF  CEMENT  MORTARS 

68.  Strength. — The  strength  of  a  mortar  is  measured 
by  its  resistance  to  tensile,  compressive,  cross-breaking, 
and  shearing  stresses,  and  also  by  determinations  of  its 
adhesion  to  inert  surfaces,  its  resistance  to  impact,  abrasion, 
etc.  In  masonry  construction,  although  mortar  is  generally 
subjected  only  to  compressive  stress,  it  is  also  at  times 
called  on  to  withstand  stresses  of  tension,  cross-breaking, 
and  shear.  Therefore,  in  practical  design,  it  is  necessary  to 
know  the  resistance  of  mortar  to  each  of  these  forms  of  stress. 
There  is  no  definitely  fixed  ratio  between  the  strengths  of 
mortar  subjected  to  these  different  stresses,  but  there  is 
nevertheless  a  close  relation  between  them,  so  that,  practically, 
it  may  be  assumed  that  if  a  mortar  shows  either  abnormally 
high  or  low  values  in  any  one  test,  the  same  relation  will 
develop  when  tested  under  other  stresses.  In  practice, 
therefore,  the  strength  of  mortar  is  commonly  determined 

TABLE  III 


TENSILE  STRENGTH  OF  CEMENT  MORTARS 


Proportions 

Tensile  Strength,  in  Pounds  per  Square  Inch 

Portland  Cement 

Natural  Cement 

Cement 

Parts 

Sand 

Parts 

7  Days 

28  Days 

3  Months 

7  Days 

28  Days 

3  Months 

I 

I 

45° 

600 

610 

160 

245 

280 

I 

2 

280 

38° 

395 

115 

I75 

2I5 

I 

3 

170 

245 

280 

85 

130 

^5 

I 

4 

!2S 

180 

220 

60 

IOO 

J35 

I 

5 

80 

140 

175 

40 

75 

1 10 

I 

6 

50 

115 

145 

25 

60 

90 

I 

7 

3° 

95 

120 

15 

5o 

75 

I 

8 

20 

70 

IOO 

10 

45 

65 

2G 


SANDS  AND  CEMENTS 


§29 


through  its  resistance  to  tensile  stresses,  and  its  resistance 
to  other  forms  of  stress  is  computed  from  these  results. 

69.  The  tensile  strength  of  mortar  has  been  shown  to 
vary  with  the  character  of  its  ingredients,  with  its  consistency, 
its  age,  and  with  many  other  factors.  In  Table  III  is  given 
a  fair  average  of  the  tensile  strength  that  may  be  expected 
from  mortars  of  Portland  and  natural  cements  that  are 
made  in  the  field  and  with  a  sand  of  fair  quality  but  not 
especially  prepared. 

The  strength  of  Portland-cement  mortar  increases  up  to 
about  3  months;  after  that  period,  it  remains  practically 
constant  for  an  indefinite  time.  Natural-cement  mortar, 
on  the  other  hand,  continues  to  increase  in  strength  for  2  or 
3  years,  its  ultimate  strength  being  about  25  per  cent,  in 
excess  of  that  attained  in  3  months.  The  strength  of  slag- 
cement  mortar  averages  about  three-quarters  of  that  of 
Portland-cement  mortar. 

70.  The  compressive  strength  of  cement  mortars  is 
usually  given  in  textbooks  as  being  from  eight  to  ten  times 
the  tensile  strength.  This  value  is  rather  high  for  the  average 
mortar,  a  ratio  of  from  6  to  8  being  one  more  nearly  realized 
in  practice.  The  ratio  increases  with  the  age  and  richness 
of  the  mortar,  and  varies  considerably  with  the  quality  of 
the  sand.  Portland-cement  mortars  of  1-3  mixture  that 
are  3  months  old  develop,  on  an  average,  a  compressive 
strength  of  about  1,800  pounds  per  square  inch,  while  1-2 
natural-cement  mortars  average  about  1,600  pounds. 

The  strength  of  mortars  in  cross-breaking  and  shear  may 
be  taken  at  about  one  and  one-half  to  two  times  the  tensile 
strength,  with  a  fair  amount  of  accuracy. 

71.  The  adhesion  of  mortars  to  inert  materials  varies 
both  with  the  character  of  the  mortar  and  with  the  roughness 
and  porosity  of  the  surfaces  with  which  they  are  in  contact. 
The  adhesion  of  1-2  Portland-cement  mortar,  28  days  old, 
to  sandstone  averages  about  100  pounds  per  square  inch; 
to  limestone,  75  pounds;  to  brick,  60  pounds;  to  glass, 


SANDS  AND  CEMENTS 


27 


§  29 


50  pounds;  and  to  iron  or  steel,  75  to  125  pounds.  Natural- 
cement  mortars  have  nearly  the  same  adhesive  strength  as 
those  made  of  Portland  cement. 

72.  The  resistance  to  abrasion  is  difficult  to  measure 
exactly,  but  experiments  appear  to  show  that  mortars  of  all 
cements  develop  the  best  resistance  to  abrasion  when  mixed 
in  the  proportion  of  1-2.  Sidewalks  and  similar  construc¬ 
tions,  therefore,  are  usually  made  of  this  mixture. 

73.  Lime-Cement  Mortars. — In  bricklaying  and  in 
other  places  in  which  mortar  is  employed,  it  is  frequently 
desired  to  use  a  material  that  is  more  plastic  or  smoother 
than  pure  cement  mortar.  This  quality  is  usually  obtained 
by  adding  from  10  to  25  per  cent,  of  lime  to  the  mortar. 
This  addition  of  lime  not  only  renders  the  mortar  more 
plastic,  and  hence  easier  to  work,  but  also  increases  both  its 
adhesive  strength  and  its  density,  which  assists  in  making 
the  mortar  waterproof.  The  strength'  of  cement  mortars, 
moreover,  is  generally  increased  by  small  additions  of  lime, 
such  as  10  per  cent.,  while  even  25  per  cent,  causes  no  sensible 
weakening. 

•  Great  care  should  be  taken  that  the  lime  is.  thoroughly 
slaked  when  used  in  this  manner,  for  any  unslaked  particles 
may.  through  their  expansion,  ultimately  cause  disinte¬ 
gration  of  the  mortar.  For  this  reason,  hydrated  lime  is  to 
be  preferred  for  use  in  cement  mortar,  because  its  complete 
slaking  is  assured.  Hydrated  lime  may  also  be  more  readily 
handled  and  measured  on  the  work. 

Occasionally,  small  quantities  of  cement  are  added  to 
lime  mortars  so  as  to  make  them  set  quicker  and  to  increase 
their  strength.  Such  mixtures,  however,  are  not  especially 
economical  nor  are  they  convenient  in  practice.  For  these 
reasons,  they  are  very  seldom  employed. 

74.  Retemperlng. — Sometimes,  during  building  oper¬ 
ations,  more  mortar  is  mixed  than  is  required  for  immediate 
use,  and  for  this  or  some  other  reason  batches  of  it  are  allowed 
to  stand.  In  such  cases,  mortar  composed  of  cement,  sand, 


28 


SANDS  AND  CEMENTS 


§29 


and  water  soon  begins  to  set  and  finally  becomes  hard. 
Thus,  when  it  is  desired  to  use  this  material,  more  water  has 
to  be  added  and  the  mixture  worked  until  it  again  becomes 
plastic.  This  process  is  called  retempering.  Laboratory 
tests  generally  show  that  retempering  slightly  increases  the 
strength  of  mortar,  but  the  reworking  is  more  thorough  as 
a  rule  in  the  laboratory  than  would  be  the  case  in  actual 
work.  Any  part  of  the  hardened  mortar  that  is  not  retem¬ 
pered  is  a  source  of  weakness  when  incorporated  in  the 
building.  The  adhesive  strength  of  cement,  moreover,  is 
greatly  diminished  by  this  process.  For  these  reasons, 
it  is  generally  inadvisable  to  permit  the  use  of  retempered 
mortars;  but  if  they  are  allowed,  great  care  should  be  taken 
to  see  that  the  second  working  is  thorough  and  complete. 

75.  Laying  Mortar  in  Freezing  Weather. — Frost  or 

even  cold  has  a  tendency  to  retard  greatly  the  set  of  cement 
mortars.  When  the  temperature,  moreover,  is  so  low  that 
the  water  with  which  the  mortar  is  mixed  freezes  before  it 
combines  with  the  cement,  it  may,  if  care  is  not  exercised, 
result  in  complete  destruction  of  the  work.  A  single  freezing 
is  not  particularly  harmful,  because  when  thawing  occurs, 
the  arrested  chemical  action  continues.  A  succession  of 
alternate  freezings  and  thawings,  however,  is  extremely 
injurious.  Nevertheless,  Portland-cement  mortars  may  be 
laid  even  under  the  worst  conditions  if  certain  precautions 
are  observed,  but  mortars  of  natural  cement  should  never 
be  used  in  extremely  cold  weather,  as  they  are  generally 
completely  ruined  by  freezing. 

The  bad  results  that  arise  during  mild  frost  may  be  success¬ 
fully  guarded  against  by  heating  the  sand  and  water  and  by 
using  a  quick-setting  cement  mixed  rich  and  as  dry  as  possible. 
In  extremely  cold  weather,  salt  must  be  added  to  the  water, 
so  as  to  convert  it  into  a  brine  that  requires  a  temperature 
lower  than  32°  F.  to  freeze  it.  The  common  rule  for  adding 
salt  is  to  use  a  quantity  equal  to  1  per  cent,  of  the  weight  of 
the  water  for  each  degree  of  temperature  that  is  expected 
below  33°  F.  Thus,  at  32°  F.,  a  1-per-cent,  solution  would 


§29 


SANDS  AND  CEMENTS 


29 


be  used,  while  at  25°,  an  8-per-cent,  solution  would  be  required. 
Solutions  greater  than  12  per  cent,  should  not  be  employed, 
and  if  a  temperature  below  20°  F.  is  expected,-  heat  must 
be  used  in  addition  to  the  salt.  The  finished  work  should 
also  be  protected  with  canvas  or  straw.  Manure  should 
not  be  used  for  this  purpose,  because  the  acids  it  contains 
tend  to  rot  the  cement.  Unless  the  conditions  are  such 
as  to  make  it  imperative,  it  is  not  advisable  to  lay  mortars 
during  freezing  weather. 

76.  Shrinkage. — Cement  mixtures  exposed  to  the  air 
shrink  somewhat  during  the  process  of  hardening,  while 
those  immersed  in  water  tend  to  expand.  The  shrinkage  of 
ordinary  cement  mortars  is  slight,  and  when  they  are  used 
as  a  bonding  material  it  need  not  be  considered.  When  used 
as  a  monolith,  as  in  sidewalks,  shrinkage,  as  well  as  temper¬ 
ature  changes,  is  to  some  extent  guarded  against  by  means  of 
expansion  joints.  However,  in  such  cases,  the  best  plan  is 
to  keep  the  mortar  wet  during  setting.  This  can  be  done 
by  means  of  moist  straw  or  by  sprinkling  the  mixture  with 
water.  Water  is  the  life  of  cement  and  a  liberal  application 
of  it  during  setting  not  only  prevents  excessive  shrinkage, 
but  materially  increases  the  strength  and  durability  of 
the  mortar. 

77.  Pointing. — In  the  process  known  as  pointing,  pro¬ 
jecting  joints  of  mortar  are  formed  in  stone  masonry.  Walls 
finished  in  this  manner  have  not  only  a  better  appearance, 
but  they  are  protected  from  injury  by  frost,  as  no  water 
can  accumulate  in  the  joints.  In  pointing,  the  joints  are 
raked  out  an  inch  or  two  from  the  face  of  the  wall  and  the 
pointing  material  introduced.  The  best  pointing  mortar 
is  made  of  Portland  cement  mixed  with  1  or  2  parts  of  very 
fine  sand.  The  addition  of  a  little  lime  to  the  mortar  also 
makes  it  waterproof,  more  adhesive,  and  easier  to  work. 
The  joints  formed  in  pointing  should  be  kept  wet  for  several 
days  by  sprinkling.  Pointing  should  never  be  attempted 
in  freezing  weather. 


30 


SANDS  AND  CEMENTS 


§29 


78.  Grouting. — By  grouting  is  meant  the  process  of 
filling  spaces  in  masonry  with  a  thin,  semifluid  mixture 
known  as  grout.  This  mixture  consists  of  cement,  1  or 
2  parts  of  sand,  and  an  excess  of  water.  Grout  can  be  used 
for  filling  the  voids  in  walls  of  rubble  masonry,  for  backing 
arches  and  tunnels,  and  for  filling  the  joints  between  paving 
brick.  In  fact,  it  can  be  used  in  all  places  where  it  is  imprac¬ 
ticable  to  lay  mortar  in  the  ordinary  manner.  When  hard¬ 
ened,  grout  is  weak,  friable,  and  porous;  therefore,  it  should 
not  be  employed  if  it  can  be  avoided. 

79.  Waterproofing  of  Mortars. — All  cement  mortars 
to  a  greater  or  less  degree  absorb  water.  They  therefore  not 
only  permit  dampness  to  penetrate  a  building,  but  tend 
also  to  permit  of  destruction  by  frost.  Cement  mortars  may 
best  be  made  almost  impermeable  by  using  only  sand  that 
has  been  carefully  graded  and  by  adding  hydrated  lime. 

To  waterproof  mortars  by  other  means,  two  classes  of 
materials  may  be  made — one  to  be  used  as  a  surface  wash 
on  the  finished  building,  and  the  other  to  be  incorporated 
into  the  mortar  while  it  is  being  made. 

Surface  washes  are  generally  based  either  on  a  mineral 
wax,  like  paraffin,  or  on  silicate  of  soda,  both  of  which  fill 
the  voids  in  the  mortar  and  tend  to  render  it  waterproof. 
Another  wash  that  is  often  used  consists  of  solutions  of  soap 
and  alum.  These  solutions  are  applied  alternately  and 
combine  to  form  insoluble  fatty  acids. 

The  compounds  that  are  incorporated  into  the  mortar 
while  it  is  being  made  depend,  as  a  rule,  on  the  chemical 
formation  of  a  lime  soap,  which  fills  the  interstices  of  the 
mortar.  Silicate  of  soda,  paraffin,  Japan  wax,  hydrated 
lime,  and  other  similar  materials  are  also  used.  A  water¬ 
proofing  cement  is  to  be  found  on  the  market  that  is  made 
by  introducing  wax  into  the  clinker  during  the  process 
of  manufacture. 

Practically  all  these  compounds  are  slightly  beneficial 
in  increasing  the  property  of  water  resistance,  but  carefully 
graded  sand,  as  previously  mentioned,  will  usually  produce 


$  29 


SANDS  AND  CEMENTS 


31 


far  more  effective  and  permanent  results  than  any  of  these 
compounds. 

80.  Coloring  of  Mortars. — Colors  are  often  used  in  mor¬ 
tars  to  effect  contrasts,  or  to  subdue  the  glaring  tone  of 
cement  in  sidewalks  or  in  similar  situations.  For  the  latter 
purpose,  lampblack  is  commonly  employed,  1  or  2  per  cent, 
changing  the  color  of  cement  to  gray,  or  slate.  In  order 
to  produce  architectural  effects,  colors  consisting  of  various 
mineral  substances  are  added  to  the  mortar  in  proportion  of 
from  1  to  10  per  cent.  Red  lead  weakens  mortar  and  should 
not  be  used.  The  color  of  hardened  mortar  is  quite  different 
in  appearance  from  one  that  is  still  wet,  so  that  where  it  is 
important  to  secure  the  correct  tints,  preliminary  trials 
should  be  made  until  the  proportions  desired  have  been 
determined. 

The  various  materials  employed  to  produce  different 
colors  in  mortar,  together  with  the  quantity  required  per 
barrel  of  cement,  are  as  follows:  For  gray,  2  pounds  of 
lampblack;  for  black,  45  pounds  of  manganese  dioxide; 
for  blue,  19  pounds  of  ultramarine;  for  red,  22  pounds  of  iron 
oxide;  for  bright  red,  22  pounds  of  Pompeian  or  English  red; 
and  for  violet,  22  pounds  of  violet  oxide  of  iron. 


• 

. 

. 

.  * 

. 


■ 

PLAIN  CONCRETE 


MATERIALS  USED  IN  CONCRETE 


DEFINITIONS  AND  TERMS 

1.  Concrete  is  usually  made  of  cement,  sand,  and  broken 
stone.  The  cement  in  a  plastic  state,  either  by  itself  or  with 
the  sand  that  is  generally  mixed  with  it,  is  called  the  matrix, 
while  the  broken  stone,  gravel,  or  other  material  used  as  a 
filler  is  called  the  aggregate.  The  sand  is  correctly  classed 
as  a  part  of  the  aggregate,  although  some  engineers  include  it 
with  the  matrix.  The  aggregate  is  used  to  cheapen  concrete. 
Pure,  or  neat ,  cement,  when  wet  with  water,  would  in  a  way 
fulfil  all  the  physical  requirements  of  concrete,  but  it  would 
be  too  expensive. 

2.  In  the  concrete  of  today,  hydraulic  cement  is  used 
almost  exclusively.  For  this  reason,  the  term  concrete ,  as 
commonly  used,  refers  only  to  that  variety.  In  specifying 
any  other  kind  of  concrete,  the  usual  custom  is  to  mention  it 
by  its  full  name,  as  bituminous  concrete ,  lime  concrete ,  etc. 
Such  varieties,  however,  are  of  comparatively  little  impor¬ 
tance,  and  will  not  be  treated  here. 

The  term  concrete,  besides  being  restricted  to  hydraulic- 
cement  concrete,  has  another  restriction:  the  aggregate  must 
not  be  sand  alone,  although  it  may  be  partly  sand.  A  mix¬ 
ture  of  hydraulic  cement,  sand,  and  water  is  called  by  the 
special  name  of  mortar. 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS’  HALL,  LONDON 

§  30 


211—4 


2 


PLAIN  CONCRETE 


§30 


Concrete  is  usually  named  from  the  kind  of  aggregate  used. 
For  example,  stone  concrete  embodies  the  use  of  broken 
stone  or  coarse  pebbles,  while  in  cinder  concrete,  the  aggre¬ 
gate  consists  of  cinders  or  broken  slag. 

3.  The  proportions  of  the  several  ingredients  used  in 
mixing  concrete  depend  on  the  purpose  for  which  the  concrete 
is  to  be  used,  as  well  as  on  the  strength-resisting  properties 
required  by  the  construction.  The  proportion  of  cement  and 
sand  to  the  broken  stone  depends  on  the  spaces  between  the 
stones,  which  are  known  as  voids.  In  all  instances,  there 
must  be  sufficient  mortar  to  till  the  voids  entirelv  and  to 
cover  all  surfaces  of  the  separate  stones. 

All  concrete  in  use  in  modern  construction  has  the  property 
of  hardening,  or  setting,  either  under  water  or  in  the  air. 
Concrete  is  now  extensively  used  for  all  important  foundation 
construction,  and  to  a  large  extent  in  the  erection  of  rein- 
forced-concrete  buildings  and  engineering  structures. 


CEMENT  MORTAR 

4.  Portland  cement  is  almost  exclusively  used  for  making 
concrete,  and  is  extensively  manufactured  for  that  purpose. 
In  general,  Portland  cement  is  made  by  mixing  limestone  and 
clay  materials  and  grinding  to  a  fine  powder.  The  mixture 
is  then  calcined,  or  clinkered,  in  a  rotary  kiln  at  a  high 
temperature.  The  clinkers  are  then  ground  to  make  the 
commercial  cement.  Portland  cement  possesses  the  valuable 
property  of  hardening,  or  setting,  when  mixed  with  w’ater. 
This  action  of  setting  is  not  a  drying  process,  but  is  a  chemical 
action  that  takes  place  between  the  ingredients  of  the  cement 
and  water. 

The  sand  used  in  making  cement  mortar  or  concrete  .should 
be  a  good,  clean,  river  sand,  though  as  a  substitute  for  sand 
a  clean  gravel  may  be  used  without  impairing  the  strength 
of  the  mortar  or  the  concrete.  Both  of  these  materials  are 
treated  at  length  in  Sands  and  Cements  and  in  Tests  on 
Cement. 


PLAIN  CONCRETE 


3 


§30 


The  .mixture  of  Portland  cement  with  sand  and  water  forms 
a  mortar,  which  is  the  cementing  material  of  concrete.  This 
mortar  holds  and  binds  together  the  broken  stone  that  is 
used,  and  fills  the  voids  between  the  separate  pieces.  As  the 
mortar  composed  of  the  cement  and  sand  is  the  cementing 
material  to  the  broken  stone,  so  is  the  neat  cement  to  the 
sand,  cementing  the  smaller  particles  together. 


AGGREGATES  OTHER  THAN  SAND 

5.  Desirable  Properties. — The  aggregates  or  broken 
stone  used  in  concrete  work  should  possess  three  qualities: 
(1)  They  should  be  hard  and  strong,  so  as  to  resist  crushing 
and  shearing  or  transverse  stresses;  (2)  they  should  have 
surface  texture  that  will  permit  the  cement  mortar  to  adhere 
to  their  surfaces;  and  (3)  where  the  concrete  is  to  be  used 
for  building  construction,  such  as  in  reinforced-concrete  work, 
and  for  fireproofing,  they  should  possess  refractory,  or  fire- 
resisting,  qualities.  Usually,  aggregates  that  break  in  such 
a  way  as  to  allow  the  smallest  spaces,  or  interstices,  between 
the  particles,  will  make  the  strongest  concrete  for  construction 
purposes  because  the  voids  can  be  most  economically  filled 
with  cement  mortar. 

6.  Size  of  Aggregates. — In  measuring  broken  stone, 
the  size  of  the  stone  is  determined  by  the  size  of  the  ring 
through  which  it  will  pass.  For  instance,  a  2-inch  stone 
is  one  that  will  pass  through  a  ring,  or  hole,  that  is  2  inches 
in  diameter.  In  Figs.  1,  2,  3,  4,  and  5,  the  several  sizes  of 
broken  stone  ordinarily  used  ill  concrete  work  are  shown, 
full  size,  compared  with  a  washer  that  is  2  inches  in  diameter 
and  has  a  1-inch  hole  in  the  center.  These  illustrations  are 
here  given  to  show  how  deceptive  the  actual  sizes  of  broken 
stone  may  be.  The  broken  stone  shown  in  Fig.  1  is  known 
as  2 h-inch  stone;  that  in  Fig.  2,  as  2-inch  stone;  that  in  Fig.  3, 
as  1  \-inch  stone;  and  that  in  Fig.  4,  as  1-inch  stone.  The 
broken  stone  shown  in  Fig.  5  is  4  inch  and  under,  and  is 
known  as  screenings. 


Fig.  1 


4 


§30 


PLAIN  CONCRETE 


5 


The  broken  stone  used  in  concrete  work  varies  in  size  with 
the  nature  of  the  work.  For  foundation  and  mass  construc¬ 
tion,  it  is  the  custom  to  use  broken  stone  of  a  size  that  will 


Fig.  2 


pass  through  the  2-  or  2^-inch  ring.  For  filling  the  spandrels 
of  bridges  or  the  spaces  between  walls,  where  mere  mass  is 
desired,  broken  stone  of  a  much  larger  size  is  used. 


6 


PLAIN  CONCRETE 


§30 


7.  In  reinforced-concrete  work,  the  broken  stone  must 
be  small,  owing  to  the  narrow  spaces  in  the  forms  and  to  the 
fact  that  the  concrete  mass  must  penetrate  to  all  parts  of 
the  mold  and  fill  in  around  all  the  numerous  reinforcing  rods. 


Fig.  3 


For  columns  and  wall  work,  stone  that  will  pass  through  a 
1-  or  f-inch  ring  is  suitable,  while  for  filling  the  beam  and 
girder  forms,  where  numerous  reinforcing  rods  occur,  the 
broken  stone  is  sometimes  so  small  as  to  pass  through  a 
^-inch  ring.  It  is  sometimes  specified  that  the  broken  stone 


PLAIN  CONCRETE 


7 


§30 

used  for  concrete  work  near  the  bottom  of  beams  and  girders 
shall  pass  through  a  Winch  ring,  and  that  the  balance  of  the 
broken  stone  used  in  the  beams  and  girders  shall  be  of  a  size 
that  will  pass  through  a  f-inch  ring.  It  is  hardly  practicable, 
however,  to  use  two  grades  of  mixture  in  filling  the  forms 
for  concrete  construction;  therefore,  it  is  advisable,  where 


Fig.  4 

the  beams  are  narrow  and  where  considerable  reinforcement 
is  employed,  to  use  a  small  size  of  aggregate  throughout. 

8.  The  latest  practice  in  making  concrete  is  to  use  stone 
as  it  comes  from  the  crusher,  without  screening  it.  While 
such  stone,  termed  the  run  of  crusher ,  contains  broken  stone 
of  a  size  specified,  it  also  has  smaller  particles  of  stone  and 
such  stone  dust  as  is  carried  along  with  the  broken  stone 


8  PLAIN  CONCRETE  §  30 

from  the  crusher.  Where  the  run  of  crusher  is  used,  the 
proportion  of  the  cement  and  sand  must  be  changed,  because 
the  stone  dust  takes  the  place  of  sand ;  and  if  mixed  with  the 
broken  stone,  using  the  same  proportion  as  was  specified  for 


Fig.  5 

clean  broken  stone,  a  much  poorer  concrete  will  result.  In 
using  run  of  crusher  the  very  finest  dust  should  be  washed 
or  screened  out,  as  it  tends  to  coat  the  large  pieces  and 
prevent  the  cement  from  adhering  to  them. 


§30 


PLAIN  CONCRETE 


9 


9.  Selection  of  Aggregates. — Usually,  the  character 
of  the  aggregate  used  in  mixing  concrete  depends  on  the 
availability  of  the  supply;  that  is,  in  each  locality  there  are 
places  from  which  broken  stone  or  gravel  may  be  secured  at 
a  minimum  cost,  and  this  determines  the  use  of  the  par¬ 
ticular  aggregate  for  the  concrete  to  be  used  in  that  locality. 
Where  there  is  much  choice  in  the  selection  of  the  aggregates, 
those  which  are  hardest  and  which  break  with  a  cubical 
fracture  will  make  the  best  concrete,  although  rounded 
pebbles  are  considered  by  some  engineers  to  possess  great 
advantages.  The  claim  of  these  engineers  is  that  such  stones 
pack  more  closely  together  and  embed  more  perfectly  than 
sharper  or  more  angular  stones,  so  that  while  the  concrete 

in  which  pebbles  are  employed  is  inferior  in  strength  after 

» 

three  months  to  concrete  in  which  trap  or  broken  rock  has 
been  used,  at  the  end  of  a  year  the  concrete  with  pebbles 
will  assume  greater  strength. 

10.  The  size  of  the  aggregate  has  much  to  do  with  the 
quality  and  strength  of  the  concrete.  In  mass  work,  aggre¬ 
gate  of  the  largest  size  that  it  is  possible  to  work  should  be 
used,  but  in  all  instances  the  aggregate  must  be  proportioned 
to  the  work.  For  instance,  in  heavy  retaining-wall  work, 
aggregates,  or  broken  stone,  that  will  pass  through  a  3-inch 
ring  could  well  be  used,  but  such  broken  stone  would  be 
entirely  impracticable  for  reinforeed-concrete  floor  con¬ 
struction  or  for  thin  partitions  or  walls. 

It  can,  however,  be  stated  as  a  general  proposition  that  the 
larger  the  stones,  up  to  about  3  inches,  the  stronger  will  be 
the  concrete.  This  fact  is  clearly  shown  by  Table  I,  which 
gives  the  results  of  tests  made  at  the  Watertown  Arsenal  in 
1898,  and  published  by  the  United  States  government.  The 
general  increase  in  strength  with  the  increase  in  size  of  broken 
stone  or  gravel  used  will  be  noted.  It  is  also  interesting  to 
note  that  the  concrete  becomes  heavier  per  cubic  foot,  or, 
in  other  words,  more  dense,  the  larger  the  stone  used.  This 
is,  as  would  be  expected,  because  the  stronger  the  concrete 
is,  the  less  voids,  or  air  spaces,  it  has  in  it.  All  these  tests 


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§  30 


PLAIN  CONCRETE 


11 


were  made  with  concrete  manufactured  in  the  proportion  of 
1  part  of  cement,  1  part  of  sand,  and  3  parts  of  broken  stones, 
or  a  1-1-3  (1  to  1  to  3)  mixture,  as  it  is  usually  expressed. 
It  should  be  observed  that  the  proportion  of  ingredients  is 
customarily  indicated  in  the  form  of  a  continued  ratio  con¬ 
sisting  of  three  terms,  the  first  of  which  indicates  the  quantity 
of  cement;  the  second,  the  corresponding  quantity  of  sand; 
and  the  third,  the  corresponding  quantity  of  broken  stone  or 
whatever  takes  its  place.  These  quantities  are  usually 
measured  by  volume  and  not  by  weight.  The  figures  on 
cinder  concrete  given  in  Table  I  are  added  simply  to  give  a 
comparison  of  weights,  for  it  will  be  noted  that  the  cinder 
concrete  is  older  than  the  other  concretes  and  therefore 
stronger  in  proportion. 

11.  Aggregates  that  consist  of  stone  of  varying  sizes  are 
best  for  making  concrete,  owing  to  the  fact  that  they  pack 
closer.  It  is  well,  however,  to  screen  all  the  fine  particles, 
such  as  ^-inch  sizes,  and  use  them  with  the  sand,  as  otherwise 
they  will  not  mix  properly  with  the  cement. 

Gravel  is  always  a  desirable  aggregate,  provided  it  is  clean 
and  free  from  coatings  of  clay  or  loam.  That  such  impurities 
materially  lessen  the  strength  of  the  concrete  has  been  proved 
by  tests  made  by  the  Boston  Transit  Commission.  These 
tests  show  that  compared  to  a  crushing  strength  of  605  pounds 
for.  a  concrete  made  of  clean  gravel,  there  was  a  strength  of 
only  446  pounds  for  concrete  mixed  in  the  same  proportion 
in  which  a  gravel  containing  a  percentage  of  clay  was  used. 

12.  Comparative  Values  of  Aggregates. — In  general, 
the  harder  the  aggregate  the  stronger  will  be  the  concrete 
under  compression.  The  hardness  of  the  aggregate  is  also 
an  indication  of  its  value  for  making  the  concrete,  provided 
it  is  of  a  shape  in  its  fracture  that  approaches  the  cubical 
rather  than  the  laminated,  or  flaky,  shape.  Broken  trap  rock 
is  the  best  aggregate  for  concrete  work,  the  next  in  value  is 
broken  granite,  while  the  third  in  order  of  merit  is  good 
clean  gravel.  In  fact,  these  three  aggregates  can  be  classified 
together,  and  the  item  of  cost  only  should  influence  the  selec- 


12 


PLAIN  CONCRETE 


.§30 


tion  of  any  one  of  them.  Marble,  limestone,  and  slag  make 
good  aggregates,  in  the  order  named,  there  being  objections 
to  marble  and  limestone  where  the  concrete  is  used  as  a 
fireproofing.  The  poorest  aggregates  are  sandstone,  slate, 
and  shale.  The  sandstone  is  inefficient  on  account  of  its  lack 
of  hardness  and  its  liability  to  crumble,  and  from  the  fact 
that  its  surface  is  likely  to  be  unstable.  Slate  and  shale  are 
hard,  but  they  are  of  a  laminated  structure  and  break  in  such 
flaky  shapes  that  they  will  not  pack  closely.  Cinders  are 
frequently  used  as  the  aggregate  for  concrete.  Cinder  con¬ 
crete,  however,  does  not  possess  sufficient  strength  for  struc¬ 
tural  purposes,  and  is  generally  used  for  filling  or  for 
fireproofing. 

TABLE  II 

COMPARATIVE  VALUE  OF  DIFFERENT 
AGGREGATES  USED  IN  CONCRETE 


Material 

Value 

Trap  rock . 

IOO 

Granite . 

90 

Gravel  (quartz) . 

90 

Limestone  (hard,  like  marble) .  . 

80 

Limestone  (soft) . 

75 

Slag . 

75 

Slate  . 

60 

Shale . 

55 

Cinders . 

5° 

13.  Based  on  percentages  of  efficiency,  with  trap  rock 
taken  at  100,  Table  II  gives  a  fair  representation  of  the  com¬ 
parative  values  of  the  different  aggregates.  In  considering 
the  table,  however,  the  purpose  for  which  the  concrete  is  to 
be  used  should  enter  largely  into  the  selection.  In  some  con¬ 
structions,  the  cinder  concrete  answers  the  purpose  as  well 
as,  or  better  than  stone  concrete,  and  the  cost  and  avail¬ 
ability  of  the  material  will  frequently  decide  the  selection. 


$  30 


PLAIN  CONCRETE 


13 


14.  Trap  Rock. — As  already  stated,  trap  rock  makes 
the  best  aggregates  for  concrete  work.  This  rock  breaks 
into  sharp,  angular  pieces,  is  fine  grained,  and  is  of  free  frac¬ 
ture,  without  laminated,  or  scaling,  surfaces.  It  is  an  exceed¬ 
ingly  hard,  clean,  flint-like  stone. 

Trap  rock  is  especially  good  for  reinforced-concrete  con¬ 
struction  in  that  it  possesses  great  crushing  strength  and 
considerable  transverse  resistance,  and  tends  to  increase  the 
strength  of  the  concrete  in  shear.  Owing  to  the  texture  of 
the  stone,  the  cement  adheres  strongly  to  it  and  thus  tends 
to  increase  the  tensile  strength  of  the  concrete. 

15.  Broken,  or  Crushed,  Granite. — In  some  locali¬ 
ties,  it  is  the  practice  to  break  granite  spalls  so  as  to  form 
the  aggregates  for  concrete  construction.  Broken  granite 
is  an  excellent  material  to  use  in  making  concrete.  It  has 
the  same  advantages  as  trap  rock,  except  that  it  is  not  so 
refractory  to  fire,  being  more  liable  to  split  or  break  suddenly 
under  intense  heat.  For  foundation  work,  it  is  equally  as 
good  as  trap  rock,  and  can  be  more  conveniently  obtained  in 
some  localities. 

16.  Gravel,  Pebbles,  and  Broken  Boulders. — Good, 
clean,  coarse  river  gravel,  or  pebbles,  when  properly 
screened  to  the  required  size,  make  an  aggregate  that  many 
experts  consider  superior  for  structural  concrete.  From 
experiments,  it  is  found  that  the  adhesion  of  cement  mortar 
to  the  smooth,  round  surface  of  gravel  or  pebbles  is  much 
greater  than  would  be  supposed.  Owing  to  their  spherical 
shape,  the  pebbles  will  lay  very  close  together  in  a  mass  and 
will  embed  well  in  the  cement. 

17.  Frequently,  cobblestones,  or  boulders,  in  broken 
form  are  used  as  the  aggregates  of  concrete.  Stone  of  this 
character  is  not  so  good  as  trap  rock  or  gravel,  but  it  pro¬ 
duces  concrete  suitable  for  most  purposes.  Owing  to  the 
irregular  shape  and  surfaces  of  such  stones,  their  particles  do 
not  lay  so  close  together  as  do  those  of  trap  rock.  Such 
stones  are  liable  to  be  of  a  coarse,  granular,  quartz-like  nature, 


14 


PLAIN  CONCRETE 


§30 


in  which  the  cohesion  is  small,  so  that  the  keying,  or  adhesion, 
between  the  cement  and  the  aggregates  is  not  so  good  as  in 
trap  rock. 

18.  Limestone. — In  many  localities,  it  is  customary 
to  use  broken  limestone  as  the  aggregates  of  concrete 
work.  Limestone  makes  a  good  foundation  concrete,  but 
it  is  not  advisable  to  use  it,  or  any  stone  containing  calcium 
carbonate  for  fireproofing  or  for  reinforced-concrete  building 
construction.  Reason  for  this  exists  in  the  fact  that  such 
stone,  while  it  will  admirably  resist  heat  up  to  about  1,000°  F., 
will  calcine  above  this  temperature,  forming  lime,  which, 
in  breaking  down,  will  destroy  the  strength  of  concrete.  The 
building  departments  of  many  of  the  large  cities  will  not 
permit  the  use  of  limestone  for  reinforced-concrete  con¬ 
struction. 

19.  Slag. — Good,  clean,  blast-furnace  slag  makes  a 
concrete  that  is  not  greatly  inferior  in  strength  to  one  in 
which  stone  is  used.  As  some  of  the  surfaces  of  slag  are 
vitrified,  or  glazed,  the  adhesion  of  the  cement  is  not  so  strong 
as  when  broken  stone  is  used,  so  that  the  concrete  loses  in 
tensile  and  shearing  strengths.  Besides,  the  slag  is  likely 
to  contain  a  great  deal  of  sulphur,  which,  while  it  affects  the 
cement  only  to  a  limited  extent,  is  inclined  to  cause  the  iron 
or  steel  embedded  in  it  to  corrode,  unless  such  material  is 
thoroughly  covered  with  the  cement.  Furnace  slag  is  not 
available  in  every  locality. 

20.  Shale  and  Slate. — As  a  rule,  a  shaly  rock,  which 
is  usually  found  in  stratum  formation,  does  not  make  a  good 
aggregate  for  concrete  work.  The  particles,  in  breaking,  are 
liable  to  break  along  lines  of  cleavage  in  parallel  planes,  so 
that  the  particles  are  in  the  form  of  slivers,  with  little  thick¬ 
ness  and  body.  Such  aggregates  are  not  good  for  concrete 
work,  because  the  voids  are  likely  to  be  excessive.  Besides, 
the  concrete  will  not  pack  so  closely  as  concrete  made  with 
aggregates  approaching  a  more  cubical  form.  Frequently,  in 
using  shale,  a  large  quantity  of  rotten  rock  is  found  in  the 


§30 


PLAIN  CONCRETE 


15 


aggregates.  This  rotten  rock  has  little  strength  and  is  not 
good  for  reinforced-concrete  work. 

Broken  slate  is  open  to  the  same  objections  as  shale, 
though  it  is  likely  to  be  cleaner  and  freer  from  rotten  rock. 
It  is  seldom  used  in  concrete  work,  and  would  only  be  con¬ 
sidered  as  an  aggregate  where  the  locality  determines  it  to 
be  the  most  available  material. 

21.  Cinders. — Concrete  in  which  cinders  are  employed 
as  the  aggregate  is  always  inferior  in  strength  to  broken- 
stone  concrete.  Cinders  should  not  be  used  except  as  a 
filling  material,  as  on  the  top  of  terra-cotta  arches,  or  for 
the  construction  of  very  light  reinforced-concrete  work,  such 
as  the  floor  of  fire-escape  balconies  and  other  work  of  this 
character. 

Only  clean  cinders,  and,  preferably,  those  from  the  furnace 
of  a  steam  boiler,  should  be  used  for  making  concrete.  It  is 
best  to  screen  the  cinders,  so  that  the  concrete  will  not  be 
made  lean  by  the  fine  particles  when  mixed  with  mortar 
already  containing  sand. 

The  principal  advantage  of  cinder  concrete  is  that  it  is 
light  in  weight.  It  does  not  compare  favorably  with  stone 
concrete,  on  account  of  its  inferior  strength,  and  because  it 
is  likely,  in  lean  mixtures,  to  cause  corroding  of  steel  or  iron. 


PROPORTIONING  OF  INGREDIENTS 

22.  Effect  on  Strength  and  Imperviousness. — The 
strength  of  concrete  depends  on  the  strength  of  the  cement 
and  the  thoroughness  with  which  the  cement  binds  together 
the  various  pieces  of  the  aggregate.  The  more  completely 
the  voids  are  filled,  the  more  completely  will  the  aggregate 
be  held  together.  Therefore,  it  may  be  stated  that  the 
more  solid  and  condensed  the  concrete  is,  the  less  voids  it 
will  have,  and  the  stronger  it  will  be.  The  same  is  true  with 
regard  to  making  concrete  waterproof:  the  more  dense  the 
concrete  is,  the  more  nearly  waterproof  it  is.  When  it  is 
desired  to  make  the  concrete  more  impervious  to  water, 


16  ^  PLAIN  CONCRETE  §30 

a  greater  quantity  of  cement  is  used  in  order  that  the  voids 
in  the  sand  and  broken  stone  may  be  more  completely  filled. 
A  mixture  of  1  part  of  cement,  1^  parts  of  sand,  and  3  parts 
of  stone,  which  would  be  considered  extravagantly  rich  for 
a  dry  place,  is  probably  as  dense  a  concrete,  and  as  good 
for  waterproofing  qualities,  as  can  be  made.  It  is,  however, 
impossible  to  make  concrete  entirely  waterproof,  as  will 
be  explained  later. 

23.  As  already  stated,  the  proper  proportion  of  ingre¬ 
dients  for  the  best  concrete  is  such  that  there  will  be  enough 
cement  in  the  mixture  to  bind  all  the  materials  together, 
and  that  the  materials  will  be  of  such  various  sizes  that 
all  voids  will  be  filled.  When  a  concrete  is  made  of  cement, 
sand,  and  stone,  and  the  stone  is  of  such  a  size  that  it  will 
pass  through  a  3-ineh  ring,  but  will  not  pass  through  a 
2^-inch  ring,  the  concrete  is  weaker  and  requires  more  cement 
than  one  made  with  graded  stone  from  3  inches  down.  When 
the  stone  is  graded  in  size,  the  smaller-sized  stones  fill  the 
voids  between  the  larger  stones,  and  thus  reduce  the  quantity 
of  cement  and  sand  required.  The  grading  of  the  stone 
also  makes  the  concrete  stronger.  The  cause  of  this  increase 
of  strength  is  not  apparent,  but  numerous  experiments  have 
proved  the  fact  without  question. 

24.  It  would  seem  that  to  make  a  perfect  concrete  there 
ought  to  be  certain  fixed  proportions  of  ingredients  and  fixed 
graduations  in  the  size  of  the  aggregate,  starting  with  a 
certain  largest  size  of  stone,  and  then  a  certain  quantity  of 
stone,  say  £  inch  smaller,  and  so  on  down  to  the  different 
grades  of  sand.  This  fact  is  undoubtedly  true,  but  to  mix 
the  ingredients  in  the  proper  proportions  is  a  difficult  task, 
which  should  not  be  undertaken  except  in  work  of  great 
magnitude  and  importance.  In  practice,  the  small  stone 
chips  (except  the  very  fine  stone  dust,  which  is  always  con¬ 
sidered  injurious  to  concrete,  and  is  usually  screened  out) 
resulting  from  the  crushing  of  broken  stone  are  usually 
added  to  the  concrete.  Some  engineers  advise  that  the 
chips  be  first  screened  out  from  the  broken  stones  and 


§30 


PLAIN  CONCRETE 


17 


afterwards  added  in  known  proportions.  This  is  another 
step  in  the  right  direction.  If  all  these  precautions  were 
followed,  it  might  be  possible  to  make  a  concrete  that  would 
be  absolutely  reliable  under  given  conditions,  and  with 
a  crushing  strength  that  could  be  foretold  to  within  about 
5  per  cent. ;  but,  on  account  of  other  conditions  that  enter 
into  the  problem,  such  accuracy  cannot  be  attained.  It  is, 
therefore,  useless,  as  a  rule,  to  try  to  do  more  than  provide 
graded  stone  and  graded  sand  for  the  concrete  without 
regard  to  the  proportions  of  the  various  sizes.  The  engineer 
decides  the  proportions  of  cement  to  sand  and  broken  stone 
and  the  maximum  size  of  the  latter,  and  that  is  as  far  as  he 
usually  goes. 

25.  Proportioning  by  Voids. — In  one  method  of  pro¬ 
portioning  concrete,  the  ratio  of  cement  to  sand  is  first 
decided  on;  as,  for  example,  a  1-3  mixture  (1  part  of  cement 
to  3  of  sand).  A  certain  volume  of  broken  stone  of  a  quality 
similar  to  that  which  it  is  proposed  to  use  in  the  concrete 
is  put  in  any  vessel,  as  a  barrel,  of  known  capacity.  The 
broken  stone  must  just  fill  the  vessel.  Water  is  then  poured 
on  until  the  vessel  holds  no  more,  and  this  water,  which 
has  filled  all  the  voids  in  the  broken  stones,  is  then  run 
off  and  measured.  The  ratio  of  the  volume  of  water  to  the 
entire  volume  of  the  vessel  gives  the  proportion  of  the  voids. 
Now,  the  mixture  of  the  sand  and  cement,  which  is  assumed 
to  have  the  same  volume  as  the  sand  alone,  must  fill  the  voids 
in  the  stone.  Suppose,  for  example,  that  40  per  cent,  of  voids 
are  found;  it  is  customary  to  add  10  per  cent,  for  inaccuracy, 
so  that,  in  this  case,  the  voids  are  50  per  cent,  of  the  whole 
volume.  Therefore,  50  per  cent,  of  sand  must  be  added  to  fill 
the  voids,  and,  consequently,  the  ratio  of  the  volume  of  sand 
to  that  of  stone  is  1-2,  or  3-6.  Therefore,  the  proper  pro¬ 
portion  of  the  materials  for  the  concrete  under  consideration 
would  be  1-3-6  (1  part  cement,  3  parts  sand,  6  parts  stone). 
This  method  of  proportioning  concrete  is  not  very  accurate, 
and  is  complicated;  it  is  used  only  for  works  of  great  impor¬ 
tance,  and  is  usually  left  to  a  concrete  specialist. 

211—5 


18 


PLAIN  CONCRETE 


§30 


26.  Proportioning  by  Weights. — The  ingredients  for  a 
sample  batch  of  concrete  are  weighed  out  in  known  propor¬ 
tions  and  mixed  to  the  desired  consistency  on  a  sheet  of  steel. 
They  are  then  tamped  in  a  piece  of  10-inch  pipe  capped  at  one 
end.  The  pipe  thus  partly  filled  is  weighed,  and  subtracting 
the  weight  of  the  receptacle  a  check  is  obtained.  The  height 
of  the  concrete  in  the  pipe  is  then  measured  and  the  mixture 
dumped  out  before  it  hardens.  After  all  the  apparatus  is 
cleaned  another  batch  of  concrete  is  mixed,  using  the  same 
weight  of  water,  cement,  and  total  weight  of  sand  and  stone 
as  before,  but  a  different  ratio  of  weight  of  sand  to  weight  of 
stone.  The  height  of  this  concrete  in  the  pipe  is  measured. 
This  operation  is  repeated.  The  concrete  occupying  the  least 
volume  is  the  densest  and  strongest  that  can  be  made  with 
that  particular  sand  and  stone  as  they  are  and  with  the  given 
proportion  of  cement..  The  volumes  corresponding  to  the 
weights  can  be  found  by  trial  measurements. 

27.  Usual  Proportions  of  Materials. — It  is  not  always 

necessary  to  use  the  strongest  concrete,  as  the  concrete  may  be 
required  to  withstand  only  slight  stresses  and  simply  be  used 
for  its  weight.  The  strongest  concrete  would  then  be  unneces¬ 
sarily  expensive.  Often  the  foregoing  methods  of  proportioning 
concrete  are  not  employed  and  the  engineer  specifies  a  mixture 
from  his  own  experience  without  testing  the  aggregates  in  any 
way,  except  to  see  that  the  stone  is  under  the  specified  maximum 
size  and  properly  graded,  and  that  the  sand  is  in  large  grains, 
graded  down,  and  free  from  dirt  and  loam.  A  common  pro¬ 
portion  for  unimportant  work  is  1-3-6.  This  proportion  may 
be  used  for  foundations  below  ground,  in  engine  bases,  in  the 
foundations  for  asphalt  pavements,  and  for  similar  purposes. 
A  richer  mixture,  1-2-4,  is  used  in  piers,  in  dams,  in  important 
reinforced-concrete  work,  and  in  other  places  where  great 
strength  is  desired.  The  average  ultimate  strengths  of  such 
mixtures  are  given  later. 

28.  Water. — The  wetter  the  concrete  is,  the  easier  it 
will  be  to  put  in  place,  but  mixtures  that  are  too  wet  are 
not  so  strong  as  medium  mixtures.  The  amount  of  water 


PLAIN  CONCRETE 


19 


§  30 

that  will  make  the  best  mixture  is  such  that  after  the  con¬ 
crete  has  been  put  in  place  and  rammed  it  will  quake  like 
jelly  when  struck  with  a  spade,  and  water  will  come  to  the 
surface.  If  the  concrete  is  wetter  than  this,  the  water  will 
have  a  slight  chemical  effect  on  the  cement,  and,  moreover, 
the  sand  and  cement  will  tend  to  separate  from  the  broken 
stone. 

In  cinder  concrete,  owing  to  the  porosity  of  the  cinders, 
it  is  necessary  to  use  a  little  more  water,  so  that  the  cement 
will  be  liquid  enough  to  fill  the  little  cavities  in  each  cinder. 
This  precaution  is  indispensable  when  the  concrete  is  to 
be  used  with  steel,  as  otherwise  the  steel  will  be  rapidly 
corroded  by  the  action  of  air  reaching  it  through  the  pores 
in  the  cinder. 

29.  Dry  Concrete. — With  the  advent  of  the  concrete 
block,  a  great  deal  is  heard  about  dry  concrete.  This 
name  is  given  to  concrete  in  which  as  little  water  as  possible 
is  mixed.  In  the  concrete-block  manufacturing  business,  the 
mold  in  which  each  block  is  made  is  required  as  soon  as 
possible,  so  that  it  can  be  used  over  again  and  thus  increase 
the  capacity  of  the  machine  to  which  it  belongs.  For  this 
reason,  the  concrete-block  manufacturers  use,  as  a  rule,  dry 
concrete,  and  attempt  to  supply  the  remainder  of  the  water 
required  for  the  complete  crystallization  or  setting  of  the 
cement  by  curing  the  blocks;  that  is,  by  sprinkling  them 
with  water  for  a  week  or  so.  The  results  of  recent  tests 
seem  to  indicate  that  dry  concrete  will  show  higher  compres¬ 
sion  values  for  a  limited  time  after  it  is  made,  but  that  the 
rate  of  increase  of  strength  is  not  so  great  as  with  wet  concrete. 
After  1  year  or  6  months,  the  strength  of  the  wet  concrete 
wfill  be  found  to  have  attained,  and  perhaps  surpassed,  that 
of  the  dry  mixture. 

There  is  a  serious  objection  to  dry  concrete,  namely,  that 
it  cannot  be  rammed  to  so  dense  a  mass  as  wet  concrete. 
Therefore,  when  it  is  desired  to  make  concrete  waterproof, 
it  should  be  mixed  wet. 


20 


PLAIN  CONCRETE 


§30 


PROPERTIES  OF  CONCRETE 


GENERAL  CHARACTERISTICS 

30.  Weight  of  Concrete. — The  weight  of  concrete 
depends  on  the  character  of  the  aggregates  used  in  the  mix¬ 
ture  and  the  proportion  of  the  ingredients.  Cinder  concrete 
weighs  from  90  to  105  pounds  per  cubic  foot,  while  plain  stone 
concrete  weighs  about  140  pounds  per  cubic  foot,  and  con¬ 
crete  reinforced  with  steel  rods,  or  bars,  averages  in  the 
neighborhood  of  150  pounds  per  cubic  foot.  These  weights 

9 

are  based  on  the  usual  mixtures,  and  are  sufficiently  accurate 
for  engineering  calculations. 

31.  Corrosion  of  Steel  in  Concrete. — It  has  been 

conclusively  proved  by  experience  and  test  that  steel  or  iron 
completely  embedded  in  the  usual  mixture  of  concrete  is 
proof  against  serious  corrosion.  In  modern  construction,  an 
examination  of  iron  and  steel  bars  that  have  been  embedded 
in  concrete  subjected  to  conditions  ordinarily  favorable  to 
the  corrosion  of  metals,  has  shown  them,  after  20  years,  to 
be  practically  unaffected.  The  corrosion  of  steel  or  iron  is 
only  possible  where  the  metals  are  subjected  to  moisture 
and  carbonic-acid  gas,  or  carbon  dioxide,  chemically  known 
as  C02.  Portland  cement  contains  free  alkali,  and  steel  or 
iron  will  not  rust  in  the  presence  of  an  alkali.  Corrosion 
will  occur  only  where  the  concrete  has  been  carelessly  placed 
and  where  voids  in  the  concrete  have  exposed  the  metal. 

Wet  concrete  offers  more  protection  to  iron  or  steel  than 
a  dry  mixture,  owing  to  the  fact  that  the  metal  is  better 
coated  with  the  cement  mixture.  Cinder  concrete,  when  of 
a  rich  mixture — at  least  one  sufficiently  rich  in  cement  to 
coat  every  particle  of  the  cinder — will  protect  ironwork  or 
steelwork  as  well  as  stone  concrete;  but,  if  it  is  not  properly 


§30 


PLAIN  CONCRETE 


21 


mixed  and  particles  of  the  uncoated  coal  or  cinder  come  in 
contact  with  the  steel,  rapid  corrosion  is  likely  to  commence. 

32.  Effect  of  Fire  on  Concrete. — Concrete  is  essentially 
a  fireproof  material.  All  the  ingredients  of  which  it  is  com¬ 
posed  are  of  a  highly  refractory  nature,  the  aggregates  being 
the  elements  of  the  mixture  that  are  most  quickly  affected 
by  intense  heat.  This  is  especially  true  of  granite  and 
limestone  aggregates,  the  former  being,  likely  to  crack  or 
burst  when  heated,  and  the  latter  liable  to  calcine.  After 
cement  has  set,  the  chemical  union  of  its  particles  is  liable 
to  destruction  by  fire,  owing  to  the  fact  that  intense  heat 
robs  the  cement  of  the  water  of  crystallization,  or  dehydrates 
the  cement,  thus  softening  the  material  and  making  it 
crumbly.  If  concrete  in  a  mass  is  subjected  to  intense 
heat,  this  action  of  dehydration  extends  into  the  concrete 
only  for  a  depth  of  J  to  |  inch,  and  is  not  likely  to  penetrate 
farther.  This  dehydration  is  observed  in  the  interior  of 
concrete  stacks,  on  the  concrete  of  floor  systems  tested  for 
their  fireproof  qualities,  as  well  as  in  concrete  structures 
where  actual  conflagrations  have  occurred. 

There  is  no  better  fireproofing  material  than  concrete, 
provided  it  is  in  a  mass  surrounding  tjie  steel,  because  it  is 
a  good  non-conductor,  has  considerable  resistance  against 
destruction  by  shock,  and  has  about  the  same  coefficient  of 
expansion  as  steel.  Stone  and  cinder  concretes  also  have 
fire-resisting  qualities. 

33.  Shrinkage  of  Concrete. — All  concrete  shrinks 
when  allowed  to  set  in  air.  The  amount  of  the  shrinkage 
depends  on  the  richness  of  the  mixture  in  cement  mortar  and 
the  quantity  of  water-  used.  The  shrinkage  of  concrete  is 
principally  noticeable  in  the  filling  of  tall  column  forms,  or 
molds.  When  these  forms  are  15  or  20  feet  in  height  and 
are  filled  with  concrete,  an  appreciable  amount  of  shrinkage 
will  be  observed  in  the  setting  of  the  concrete.  The  top  surface 
of  the  concrete  will  drop  as  much  as  a  half-inch  from  the  time 
of  filling  the  forms  until  the  concrete  has  hardened,  or 
obtained  the  initial  set.  Undoubtedly  some  of  the  shrinkage 


22 


PLAIN  CONCRETE 


§30 


observed  in  concrete  work  in  the  filling  of  forms  is  only 
apparent,  the  reduction  in  volume  being  the  result  of  the 
settling  of  the  material  rather  than  its  shrinkage. 

While  experiments  on  the  shrinkage  or  expansion  of 
cement  mortar  have  been  limited,  they  show  that  all  cement 
mortars  shrink  while  setting  in  the  air  and  that  some  of  them 
swell  slightly  while  setting  under  water.  It  has  been  con¬ 
clusively  proved  that  the  richer  the  cement  mortar,  that  is, 
the  greater  the  proportion  of  cement  to  sand,  the  greater  will 
be  the  change  in  dimensions.  Considere,  a  French  concrete 
expert,  has  found  by  experiment  that  a  1-3  mortar  will 
shrink  about  .05  to  .15  per  cent,  in  setting  in  air,  and  that  the 
shrinkage  will  be  two  to  three  times  as  great  with  neat  cement. 
The  shrinkage  in  concrete  will  be  much  less  than  with  neat 
cement  or  cement  mortar,  in  the  proportion  that  the  cement 
bears  in  volume  to  the  sand  or  stone. 

The  shrinkage  of  concrete  is  lessened  by  embedding  in  it 
steel  rods  or  bars,  as  these,  by  their  tensile  resistance,  prevent 
the  shrinkage  of  the  material  in  setting.  By  the  experi¬ 
ments  of  Considere,  it  is  found  that  with  1-3  mortar  rein¬ 
forced  with  steel  the  shrinkage  in  setting  is  about  one-fifth 

that  of  the  same  mortar  without  the  steel  reinforcement. 

$ 

34.  Effect  of  Thermal  Changes  in  Concrete. — Nearly 

all  materials  expand  slightly  as  they  become  heated.  Concrete 
and  steel  also  follow  this  law.  By  the  linear  coefficient  of 
expansion  of  a  material  is  meant  the  ratio  of  the  increase  of 
length  to  the  original  length  of  the  material,  due  to  a  rise 
of  temperature  of  1°  F.  The  original  length  is  usually  meas¬ 
ured  at  a  temperature  of  32°  F.  Thus,  suppose  that  the 
length  of  a  bar  of  steel  at  32°  F.,  when  measured  with  great 
accuracy,  was  39.432  inches.  Suppose  also  that  at  a 
temperature  of  69°  F.  the  length  was  39.441  inches. 
The  increase  in  temperature,  therefore,  is  69  —  32  =  37°, 
and  the  increase  in  length  is  39.441  —  39.432  =  .009  inch. 
The  increase  of  length  per  degree  rise  of  temperature  is 
.009 37=  .000243  inch.  The  coefficient  of  expansion  is 
therefore  .000243^-39.432  =.00000616. 


PLAIN  CONCRETE 


23 


§30 

The  contraction  or  the  expansion  of  concrete  due  to  changes 
in  temperature  is  about  the  same  as  that  of  steel.  The 
average  coefficient  of  expansion  of  a  1-2-4  concrete  for  each 
Fahrenheit  degree  in  change  of  temperature  is  .0000055. 
Experiments  made  on  1-3-6  concrete  give  a  coefficient  of 
expansion  of  .0000065,  which  is  practically  the  same  as  the 
coefficient  of  steel. 

35.  Effect  of  Vibration  on  Concrete. — The  effect  of 
constant  vibration  on  concrete  structures  has  not  been 
definitely  determined.  Many  buildings  and  bridges  con¬ 
structed  of  concrete  reinforced  with  steel  rods  and  bars  have 
withstood  heavy  and  constant  vibration,  either  continuous 
or  intermittent,  for  an  extended  period  of  years  with  no 
apparent  deterioration  in  strength.  Fresh  concrete  is  always, 
however,  subject  to  deterioration  by  vibratioij,  and  the 
strength  of  concrete  subjected  to  jar  or  shock  when  setting  is 
materially  reduced,  because  the  process  of  crystallization 
between  the  particles,  and  the  consequent  cohesion  of  the 
mass,  seems  to  be  partly  destroyed. 

33.  Permeability  of  Concrete. — Concrete  as  ordinarily 
used  in  construction  is  not  waterproof.  While  a  slab  or  a 
wall  of  concrete  will  hold  back  water  for  a  few  hours,  after  the 
water  has  once  penetrated  the  mass,  it  will  run  or  drip  through 
the  concrete  with  considerable  rapidity. 

There  is  an  instance  of  a  reinforced-concrete  floor  that 
was  improperly  waterproofed  with  felt  and  pitch.  To  test 
the  floor,  it  was  covered  with  water  to  a  depth  of  several 
inches,  and  appeared  to  the  superintendent,  on  leaving  the 
work  at  night,  to  be  water-tight.  After  several  hours,  how¬ 
ever,  the  water  had  penetrated  the  inefficient  waterproofing 
material,  and  when  it  had  soaked  through  and  saturated  the 
concrete  floor  slab  it  rapidly  leaked  through  to  the  floor  below. 

Numerous  instances  of  the  permeability  of  concrete  are 
shown  in  practical  examples  of  tunnels  of  concrete  inter¬ 
cepting  springs,  and  in  concrete  arches  where  the  spandrels, 
or  backing,  are  not  properly  drained  or  waterproofed. 


24 


PLAIN  CONCRETE 


§30 


37.  From  extensive  experiments,  it  has  been  determined 
that  plain  concrete,  as  a  rule,  is  not  waterproof,  and  that 
permeability  is  greatest  where  concrete  is  poorest,  or  where 
there  is  the  least  percentage  of  cement  in  proportion  to 
the  aggregates. 

The  permeability  also  varies,  even  with  concretes  con¬ 
taining  cement  mixtures  of  the  same  proportion  but  with  a 
variation  in  the  size  or  composition  of  the  aggregates.  It 
has  been  found  that  where  the  aggregates  are  the  finest  the 
concrete  is  the  most  permeable,  and  that  where  the  aggregates 
are  about  equally  divided  between  the  fine  and  the  coarse, 
the  concrete  is  the  least  permeable.  It  has  also  been  ascer¬ 
tained  that  the  permeability  of  concrete  or  of  cement  mortars 
diminishes  as  the  leakage  continues,  and  that  the  permeability 
of  concrete  is  more  likely  to  be  diminished  by  the  use  of  a 
wet  mixture  than  one  that  is  dry. 

In  general,  therefore,  it  may  be  remarked  that  the  perme¬ 
ability  of  concrete  is  decreased  in  almost  direct  proportion  to 
the  amount  of  mortar  used  in  the  mixture. 


WORKING  STRESSES  AND  STRENGTH  VALUES  OF 

CONCRETE 

38.  Working  Stresses  of  Concrete. — The  ultimate 
strength  of  concrete  varies  so  with  the  proportion  of  the 
mixture,  manner  of  working,  character  of  ingredients,  and 
age  of  material,  that  it  is  necessary  to  assume  low  unit  working 
stresses  for  it. 

The  usual  working  stress  for  plain  concrete  under  com¬ 
pression  is  from  250  to  300  pounds  per  square  inch,  although, 
in  masses,  as  in  footings,  a  1-2^— 5  concrete  would  safely 
sustain  as  much  as  500  pounds  to  the  square  inch.  When 
reinforced  concrete  is  subjected  to  compression  from  loads 
causing  bending,  it  is  customary  to  figure  the  safe  allow¬ 
able  unit  compressive  stress  in  the  compression  portion  of  a 
reinforced-concrete  beam  at  from  500  to  600  or  even  700 
pounds  per  square  inch. 


§30 


PLAIN  CONCRETE 


25 


In  tension,  concrete  has  little  value;  in  fact,  it  cannot  be 
relied  on  to  resist  this  stress.  Generally,  the  tensile  strength 
of  plain  concrete  is  about  one-tenth  of  its  compressive  strength. 

The  modulus  of  rupture,  or  the'  unit  value  for  figuring 
the  transverse  strength  of*  plain  concrete,  is  much  lower 
than  the  modulus  of  rupture  of  any  of  the  good  building 
stones.  The  safe  unit  bending  stress  for  plain  concrete, 
based  on  a  factor  of  safety  of  4,  from  values  of  the  modulus 
of  rupture  obtained  from  recent  tests  made  on  concrete 
30  days  old,  is  about  110  pounds.  This  value  is  for  concrete 
composed  of  1  part  of  cement,  2  parts  of  sand,  and  4  parts  of 
broken  stone.  With  a  poorer  mixture,  as  a  1-2-5  concrete, 
a  safe  bending  stress  of  about  95  pounds  should  be  used, 
while  with  a  1-3-5  mixture,  the  safe  bending  stress  is  barely 
70  pounds,  and  this  value  shows  a  corresponding  decrease 
as  the  mixture  becomes  leaner. 

The  safe  unit  shearing  stress  of  plain  concrete  is,  in  practice, 
taken  at  a  very  low  figure  when  compared  with  recent  tests 
giving  the  ultimate  shearing  resistance  of  this  material. 
This  low  figure  is  probably  due  to  the  fact  that  few  tests 
have  been  made  to  determine  the  value  of  plain  concrete 
in  shear;  or  perhaps  it  is  due  to  the  unreliability  of  concrete, 
as  found  in  practice,  to  resist  this  stress.  The  conservative 
safe  unit  shearing  stress  of  plain  concrete  is  taken  at  50  pounds, 
although  the  value  may  be  increased  for  rich  mixtures  and 
careful  workmanship  to  75  pounds. 

The  safe  grip ,  or  bond,  as  it  is  called,  of  concrete  on  steel 
rods  or  bars  with  plain  surfaces  embedded  in  it,  is  taken,  for 
purposes  of  calculation,  at  50  pounds  per  square  inch  of  the 
surface  of  the  metal  in  contact  with  the  concrete. 

39.  All  the  values  just  mentioned  are  based  on  concrete 
at  least  1  month  old.  In  fact,  they  are  working  values  that 
are  assumed  to  be  safe  for  a  structure  properly  erected  and 
completed  in  this  material.  There  is  great  diversity  of 
opinion  regarding  the  safe  unit  values  of  plain  concrete, 
and  there  is  no  uniformity  in  the  building  laws  of  the  several 
cities  regarding  the  strength  of  this  material.  This  is  shown 


26 


PLAIN  CONCRETE 


§30 


by  Table  III,  which  gives  the  working  values  of  concrete 
allowed  by  the  building  laws  of  several  cities. 

TABLE  III 

UNIT  WORKING  VALUES  OF  CONCRETE  ALLOWED  BY 

VARIOUS  CITIES 


Name  of  City 

Direct 

Compression 

Pounds  per 
Square  Inch 

Shear 

Pounds  per 
Square  Inch 

Unit  Compressive  Stress 
Under  Bending  Loads 

Pounds  per  Square 
Inch 

New  York . 

35° 

5° 

5  00 

Philadelphia.  .  . 

250 

5° 

600 

Cleveland . 

400 

5° 

5°° 

San  Francisco  . 

45° 

75 

5  00 

Buffalo . 

35° 

5° 

50° 

Toronto . 

340 

5° 

5°° 

40.  Strength  Values  of  Concrete. — The  ultimate 
strength  of  concrete  in  compression,  tension,  and  shear  varies 
with  the  proportions  of  the  mixture,  the  quality  of  the 
ingredients,  and  the  manner  of  mixing.  It  also  varies  with 
the  quantity  of  water  used  and  the  conditions  existing  at  the 
time  of  mixing,  as  well  as  with  the  age  of  the  concrete.  • 

It  is  evident,  therefore,  that  only  average  values  can  be 
given,  and  only  those  for  concrete  of  the  usual  proportions 
will  be  useful.  According  to  tests  made  at  the  Watertown 
Arsenal  on  concrete  made  of  various  brands  of  cement,  a 
1-2-4  mixture  had  an  average  compressive  strength,  at  the 
end  of  1  month,  of  2,399  pounds  per  square  inch,  and  at  the 
end  of  6  months,  of  3,826  pounds  per  square  inch,  while  con¬ 
crete  of  a  1-3-6  mixture  had  average  unit  compressive  values 
of  2,164  and  3,086  pounds,  at  1  and  6  months,  respectively. 

These  values  are  higher  than  would  probably  be  realized  in 
practice,  owing  to  superior  methods  of  mixing  and  placing. 
Therefore,  an  average  unit  compressive  strength  of  2,000 
pounds*  would  be  conservative  for  a  1-2-4  concrete,  from 
1  to  3  months  old,  and  1,600  pounds  for  a  1-3-6  concrete  of 


§30 


PLAIN  CONCRETE 


27 


the  same  age.  Mixtures  varying  in  richness  between  these 
limits  would  have  proportional  values. 

41.  The  tensile  strength  of  concrete  is  frequently  stated 
as  being  about  one-tenth  of  its  compressive  resistance.  This, 
however,  is  only  true  of  some  mixtures.  Tests  to  ascertain 
the  tensile  strength  of  concrete  of  different  mixtures 
have  been  made  at  various  times.  The  results  of  these  tests, 
based  on  concrete  about  30  days  old,  vary  from  311  pounds 
per  square  inch  for  a  1-2-4  mixture  to  237  pounds  per  square 
inch  for  a  1-3-6  mixture. 

The  tensile  strength  of  concrete  is  more  affected  by  the 
quality  of  the  mixture  than  is  its  compressive  stress.  There¬ 
fore,  a  conservative  ultimate-tensile-strength  value  of  a 
1-2-4  mixture  would  be  about  200  pounds,  while  for  a  1-3-6 
mixture,  it  would  be  about  125  pounds. 

42.  The  shearing  strength  of  concrete  is  usually  much 
less  than  the  compressive  strength.  For  a  1-2-4  mixture  an 
average  ultimate  shearing  strength  of  1,480  pounds  per  square 
inch  has  been  determined  by  tests,  while  a  1-3-5  mixture 
has  given  1,180  pounds,  and  a  1-3-6  mixture  has  given  a 
value  in  shear  of  1,150  pounds  per  square  inch. 

The  average  modulus  of  rupture  for  concrete  that  was  from 
33  to  35  days  old  has  been  found  to  be  439  pounds  per  square 
inch  for  a  1-2-4  mixture,  380  pounds  per  square  inch  for  a 
1-2-5  mixture,  and  285  pounds  per  square  inch  for  a  1-3-5 
mixture,  while  a  1-3-6  mixture  gave  a  result  of  226  pounds 
per  square  inch. 

i 

43.  The  values  given  in  Table  IV  are  recommended  as 
ultimate  values  by  W.  Purves  Taylor,  engineer  in  charge  of 
the  municipal  testing  laboratory  of  Philadelphia.  The  figures 
represent  values  obtained  from  six  hundred  experiments  made 
on  concrete  properly  mixed  with  good  Portland  cement.  It 
will  be  noticed  that  the  values  given  for  shear  are  considerably 
lower  than  those  just  given  in  the  text.  The  results  obtained 
depend  to  a  large  extent  on  the  method  of  testing.  Some 
engineers  prefer  the  lower  values. 


AVERAGE  ULTIMATE  STRENGTH  OF  CONCRETE  MADE  FROM  PORTLAND  CEME 


H 

£ 


W 

% 

0 

H 

co 


H 

w 

M 

HH 

GO 

p 

S3 

P 

0 

•> 

0 

cc 


Shear 

Pounds  per  Square  Inch 

Stpuoyi  9 

<0  -t  ‘O  O  -t*  O  xo  O  OO 
h  (j\  \0  rj-  <0  >-t  OoC 

rOdddddddM 

stpjuoj^  £ 

O  m  fO  00  1-1  tTOO  po 

0000  tJ-  d  m  On  O 

COdddddMHCHl 

q;uoj\[  i 

a  +  ifioo  O  lO  00  O  io 

O  't  «  O  O'  f''  >0  *+  d 

ddddMHMHM 

sAbq  L 

O  0000  fO  O  tj-  m  io 

O  N  V)  pf)  N  o  OOO  t'- 

d  Hi  M  W  M  t-H 

Compression 

Pounds  per  Square  Inch 

sipuoj^  9 

ooooooooo 

O  io  O  00  »o  d  o  O 

»o  co  d  O  OOO  t^O  xo 

CSCNOIOJMMMMM 

sq^uoj^  £ 

OOOOOOOOO 

O  to  O  O  d  O  lo  d  o 

Tt-  d  M  OOOO  lo  't  fO 

dddHiHHHMHM 

qiuoffl  x 

ooooooooo 
to  to  O  O  d  OO  d  o 

M  OOOOXDTTd  M  O 

CNMMMMMMMM 

sAuq  4 

ooooooooo 

O  <0  to  O  00  to  vo  vo  O 

O  rt  d  m  O'  00  O  O 

HI  M  Hi  HI 

Tension 

Pounds  per  Square  Inch 

si^uopj  9 

O  to  O  CO  1-0  -f  d  o  O 
in  fPj  d  O  O'  00  t-»  O  to 

ddddWHHHH 

sq^uoj^  C 

OxoOO  d  O  xo  d  O 
tT  d  m  O'OOOvo^tfO 

dddMMH.HMH 

m;uoj^  i 

O  'O  O  O  d  OO  d  O 

M  O'  00  O  LO^td  M  O 

dtHMMMMMlHM 

sAuq  L 

O  <0X0  0  00  to  IO  to  O 

O  rj-d  m  O'  00  t>*  O  O 

M  HI  M  HI 

Proportion  of 
Ingredients 

9UO}g 

•^■LOVO  CO  ON  O  m  cs 

M  M  M 

pung 

o  xoO  to  O  to  O  to  O 
d  d  ro  <0  P  rr  io  >o  o 

^uauiaQ 

28 


i 


PLAIN  CONCRETE 


29 


§30 


MIXING  AND  WORKING  OF 
CONCRETE 


CONCRETE  MIXTURES 


CONSISTENCY  AND  PROPORTION  OF  INGREDIENTS 

44.  Consistency  of  tlie  Mixture. — In  construction 
work,  two  kinds  of  concrete  mixtures  may  be  used — one 
employing  a  considerable  quantity  of  water,  and  the  other 
using  only  sufficient  water  to  cause  the  necessary  chemical 
reaction  required  for  the  setting  of  the  cement.  The  first  is 
known  as  a  wet  mix ,  and  the  other  as  a  dry  mix. 

Wet  mix  has  the  consistency  of  very  soft  mortar,  and  is  so 
nearly  liquid  that  it  cannot  readily  be  shoveled,  but  is  poured 
into  forms.  The  forms ,  which  are  wooden  molds  into  which 
the  concrete  is  poured,  are  often  called  the  centering.  A  dry 
mix  of  concrete  is  mealy  in  consistency,  with  no  visible 
superabundance  of  moisture.  The  former  would  flow  if 
placed  on  a  mortar  board,  while  the  latter  would  remain  in 
a  pile  on  the  center  of  the  board. 

A  wet  mix  is  used  in  nearly  all  concrete  work  in  the  United 
States,  and  especially  in  the  construction  of  reinforced- 
concrete  columns  and  floor  systems.  The  advantages  of  a 
wet  mix  are  that  the  concrete  is  in  such  a  liquid  state  that 
it  can  be  poured  into  forms,  and  that  it  will  enter  all  parts 
of  the  forms  and  between  the  rods,  or  bars,  of  the  metal 
reinforcement.  In  reinforced-concrete  work  there  is  a  multi¬ 
plicity  of  steel  rods,  stirrups,  and  other  auxiliary  reinforce¬ 
ment,  and  these  are  usually  placed  so  close  together  that  it 
is  only  by  the  use  of  a  wet  mixture  that  all  of  the  voids 
between  the  metal  and  the  forms  can  be  filled.  One  dis¬ 
advantage  of  a  wet  mixture,  as  stated  in  Art.  28,  especially 


30 


PLAIN  CONCRETE 


§30 


for  concrete  wall  construction,  is  that  the  broken  stone  is  liable 
to  separate  from  the  mortar  and  form  a  honeycombed  sur¬ 
face,  or  a  line  of  demarcation,  between  the  several  layers  of 
concrete. 

45.  Proportion  of  Ingredients  in  Concrete. — The 

proportion  of  cement  to  aggregates  in  a  concrete  mixture 
determines  its  physical  characteristics  and  its  structural  uses. 
A  concrete  mixture  may  be  either  rich,  medium ,  ordinary ,  or 
lean.  In  designating  the  proportion  of  the  ingredients  in 
concrete,  it  is  customary,  as  stated  in  Art.  10,  to  use  the 
cement  as  a  unit,  naming  this  material  first,  following  with 
the  sand,  and  finishing  the  notation  with  the  proportional 
parts  of  the  aggregates.  For  instance,  1-2-4  mixture  would 
indicate  that  1  part  of  cement  is  to  be  used  to  2  parts  of  sand 
and  4  parts  of  aggregate,  the  quantities  being  measured  by 
bulk. 

46.  A  concrete  mixed  in  the  proportion  of  1  part  of  cement 
to  2  parts  of  sand  and  4  parts  of  broken  stone  is  usually  called 
a  rich,  mixture.  This  mixture  is  generally  used  for  rein- 
forced-concrete  work  and  all  important  structures  subjected 
to  great  strains  or  vibratory  loads. 

47.  A  concrete  mixed  in  the  proportion  of  1  part  of 
Portland  cement  to  parts  of  sand  and  5  parts  of  aggregates, 
known  as  a  medium  mixture,  is  commonly  used  for  mass 
concrete,  such  as  foundation  walls,  building  walls,  sidewalk 
bases,  and  machine  foundations.  This  mixture  has  also  been 
used  with  success  for  reinforced-concrete  construction,  and 
if  the  work  is  well  designed  and  the  construction  carefully 
supervised,  it  will  give  excellent  results. 

48.  For  large  masses  of  concrete,  where  the  structure 
depends  for  its  stability  on  mass,  or  weight,  rather  than  on 
compressive  or  transverse  stress,  a  mixture  of  1  part  of  cement 
to  3  parts  of  sand  and  6  parts  of  broken  stone  is  used.  This 
mixture,  which  may  be  designated  as  an  ordinary,  or 
common,  mixture  for  plain  concrete,  is  used  in  the  con¬ 
struction  of  heavy  foundations,  retaining  walls,  railroad 


§30 


PLAIN  CONCRETE 


31 


abutments  or  wing  walls,  solid  concrete  foundations  for  stacks, 
and  similar  structures. 

49.  In  heavy  engineering  work,  such  as  emplacements, 
bulkheads,  and  work  of  this  character,  a  lean  mixture  of 
concrete  is  sometimes  used.  This  mixture  is  made  up  of 
1  part  of  Portland  cement,  4  parts  of  sand,  and  7  or  8  parts 
of  broken  stone,  and  answers  every  purpose  where  mere 
weight  and  mass  are  the  requirements. 


MEASURING  AND  ESTIMATING  INGREDIENTS 

50.  Methods  of  Measuring  Ingredients. — After 
deciding  what  proportions  of  ingredients  will  be  used  for  the 
concrete,  the  engineer  must  be  able  to  calculate  the  exact 
quantity  of  each  material  that  he  must  order.  Cement  is 
bought  by  the  barrel,  but  is  usually  shipped  by  the  bag.  Four 
bags  of  Portland  cement  make  a  barrel.  Natural  cement 
comes  in  bags  of  the  same  size,  or  in  larger  bags,  three  of 
which  make  a  barrel.  An  ordinary  box  car  holds  from 
400  to  600  bags.  The  purchaser  is  charged  for  the  bags  by 
the  manufacturer,  unless  they  are  of  paper,  but  he  gets  a 
rebate  for  those  which  are  returned.  A  barrel  of  Portland 
cement  weighs  about  376  pounds,  and  a  barrel  of  natural 
cement  about  282  pounds. 

Cement  is  usually  measured  by  the  barrel  just  as  it  comes 
from  the  manufacturer,  or  as  four  bags  to  the  barrel,  while 
broken  stone  and  sand  are  measured  loose  in  a  barrel.  Port¬ 
land  cement,  after  it  is  taken  out  of  its  original  package 
and  stirred  up,  fills  a  larger  volume  than  when  packed.  It 
is  therefore  necessary  to  state  just  how  the  cement  is  to  be 
measured;  and,  as  said  before,  the  custom  is  to  measure 
it  by  the  barrel,  compact.  A  cement  barrel  contains  about 
3.8  cubic  feet. 

$  , 

51.  Fuller’s  Rule. — A  practical  rule  has  been  devised 

by  W.  B.  Fuller  whereby,  after  the  proportions  of  ingredients 
have  been  fixed,  the  quantity  of  material  for  a  certain  work 


32 


PLAIN  CONCRETE 


§30 


may  be  obtained.  It  is  called  Fuller’s  rule  for  quantities, 
and  may  be  expressed  in  mathematical  symbols  as  follows: 


Let  c  =  number  of  parts  of  cement; 

5  =  number  of  parts  of  sand ; 
g  =  number  of  parts  of  gravel  or  broken  stone ; 

C  —  number  of  barrels  of  Portland  cement  required  for 
1  cubic  yard  of  concrete; 

5  =  number  of  cubic  yards  of  sand  required  for  1  cubic 
yard  of  concrete; 

G  —  number  of  cubic  yards  of  stone  or  gravel  required 
for  1  cubic  yard  of  concrete. 

Then,  C  =  — +—  (1) 

c  +  s  +  g 

q  q 

S-  —  C  s  (2) 

27 

G  =  \ leg  (3) 

If  the  broken  stone  is  of  uniformly  large  size,  with  no 
smaller  stone  in  it,  the  voids  will  be  greater  than  if  the  stone 
were  graded.  Therefore,  5  per  cent,  must  be  added  to  each 
value  found  by  the  preceding  formulas. 


Example. — If  a  1-2-4  mixture  is  considered,  what  will  be:  (a)  the 
number  of  barrels  of  cement,  ( b )  the  number  of  cubic  yards  of  sand, 
and  (c)  the  number  of  cubic  yards  of  stone  required  for  1  cubic  yard 
of  concrete? 


Solution. — (a)  Here,  c—  1,  5  =  2,  and  g  =  4.  Substituting  these 
values  in  formula  1, 

11 

C  — - -=1.57.  Ans. 

1  +  2  +  4 

(6)  Substituting  the  values  of  C  and  5  in  formula  2, 

3  8 

5  =  -— X  1.57X2  =  .44.  Ans. 

27 


( c )  Substituting  the  values  of  C  and  g  in  formula  3, 

3  8 

<7=  -  X  1.57X4  =  .88.  Ans. 

27 


§30 


PLAIN  CONCRETE 


33 


EXAMPLES  FOR  PRACTICE 


1.  How  much  (a)  Portland  cement,  ( b )  sand,  and  ( c )  broken  stone 
will  be  required  to  make  1  cubic  yard  of  1-3-6  concrete? 

'(a)  1.10  bbl. 
Ans.<  ( b )  .46  cu.  yd. 
( c )  .93  cu.  yd. 

2.  A  certain  concrete  foundation  is  to  be  15  feet  long,  15  feet  wide, 
and  12  feet  deep.  If  a  l-2^-5  mixture  is  used,  how  much  (a)  cement, 


( b )  sand,  and  (c)  broken  stone  will  be  required? 


Ans. 


(a)  129  bbl. 

( b )  45  cu.  yd. 

( c )  91  cu.  yd. 


52.  Table  of  Quantities. — Table  V,  giving  the  quan¬ 
tities  of  ingredients  for  concrete  of  various  proportions,  has 
been  prepared  by  Edwin  Thacher.  It  will  be  noted  in  this 
table  that  the  difference  in  the  character  and  size  of  the  stone 
or  gravel  used  has  been  taken  into  account.  These  values 
will  be  found  to  agree  fairly  well  with  values  found  by  Fuller’s 
rule. 


WORKING  OF  CONCRETE 

53.  Mixing  of  Concrete. — Concrete  may  be  mixed 
either  by  hand  or  by  machine.  To  obtain  a  good  concrete, 
the  ingredients  should  be  accurately  proportioned  to  the 
requirements  of  the  specification,  and  they  should  be  thor¬ 
oughly  manipulated,  so  that  the  matrix  will  be  distributed 
equally  through  the  aggregates,  coating  all  the  surfaces  and 
forming  a  mixture  of  uniform  consistency.  The  percentage 
of  water  used  should  be  uniform  with  each  batch. 

Concrete  should  always  be  mixed  as  near  the  place  where 
it  is  to  be  used  as  practicable,  so  that  very  little  time  will 
elapse  between  the  completion  of  the  mixing  process  and  the 
placing  of  the  concrete.  In  addition  to  hastening  the  work 
of  laying,  this  arrangement  will  save  much  labor  in  conveying 
the  concrete  to  the  forms. 

54.  For  small  work,  the  concrete  should  always  be  mixed 
in  small  batches,  such  as  would  be  made  up  from  1  or  2  bags 


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35 


36 


PLAIN  CONCRETE 


§30 


of  cement.  In  mixing,  hand  work  should  be  performed  on 
a  flat,  water-tight  platform.  The  sand,  after  it  has  been 
measured,  is  spread  over  the  platform  in  an  even  layer. 
Upon  the  sand  is  placed  the  cement,  and  these  two  materials 
are  turned  over  with  shovels  at  least  three  times,  or  until  the 
uniform  color  of  the  mixture  indicates  that  they  are  thor¬ 
oughly  incorporated.  The  stones,  or  aggregates,  having 
previously  been  well  wretted,  are  then  placed  on  the  top 
of  the  mixture  of  sand  and  cement,  and  these  materials  are 
also  turned  at  least  three  times,  water  being  added  after  the 
first  turning.  The  water  should  always  be  added  in  small 
quantities.  If  a  hose  is  used  for  this  purpose,  it  should  be 
fitted  with  a  sprinkling  nozzle,  as  otherwise  much  of  the 
cement  is  liable  to  be  washed  out  of  the  mixture.  The 
concrete,  when  ready  for  placing,  should  be  of  uniform  con¬ 
sistency,  either  mealy  for  a  dry  mix  or  mushy  for  a  wet  mix. 

55.  In  large  work,  the  mixing  should  be  done  by  machine. 
The  machines  used  for  mixing  concrete  are  of  two  general 
types.  In  one,  the  materials  are  proportioned  by  laborers 
and  then  dumped  into  the  machine;  in  the  other,  they  are 
proportioned  and  mixed  automatically.  The  manner  of 
mixing  varies  with  the  type  of  machine.  Usually,  the 
machine  is  driven  by  a  steam  engine,  or  by  an  electric  motor. 
The  subject  of  machine  mixing  will  be  treated  at  length  in  a 
future  Section. 

56.  Retempering  of  Concrete. — As  the  cement-and- 
sand  mixture  of  concrete  sets  in  air  in  from  20  minutes  to 
2  hours  after  it  has  been  mixed,  as  little  time  as  possible  should 
be  lost  in  conveying  it  from  the  place  where  it  is  made  to 
the  place  where  it  is  to  be  deposited.  If  concrete  is  allowed 
to  stand  for  a  considerable  length  of  time  on  the  mixing 
board  or  in  the  bin,  the  cement  will  attain  an  initial  set  and 
the  concrete  will  become  practically  useless.  Only  as  much 
concrete  as  can  be  used  at  once  should  be  mixed  at  a  time. 

If  the  cement  of  the  concrete  has  attained  its  initial  set — 
that  is,  if  the  concrete  has  commenced  to  harden — remixing 
with  water,  or  retempering  of  concrete,  as  it  is  called, 


§30 


PLAIN  CONCRETE 


37 


should  not  be  allowed;  and  if  concrete  treated  in  this  manner 
has  been  deposited  in  the  forms,  it  should  be  taken  out  and 
removed  from  the  site  of  the  operation,  because  concrete 
cannot  be  retempered  properly,  except  in  small  quantities  for 
laboratory  tests. 

57.  Concreting  at  High  Temperatures. — If  the 

weather  is  extremely  warm,  the  stone  and  sand  are  liable  to 
become  heated  to  a  high  temperature.  Then,  in  mixing  the 
materials,  the  water  necessary  for  the  crystallization  of  the 
•  cement  is  rapidly  absorbed  by  the  stone  and  the  sand,  or  else 
rapidly  evaporated  by  contact  with  them.  Again,  the 
extreme  heat  will  hasten  the  setting  of  the  cement,  and  this 
tends  to  cause  the  concrete  to  cake  in  the  mixing  machine, 
producing  lumpy  and  inferior  concrete.  In  order  to  over¬ 
come  such  difficulties,  the  stone  should  be  thoroughly  wetted 
with  a  hose,  and  the  sand  and  stone  should  be  kept  under 
cover,  away  from  the  direct  rays  of  the  sun.  Likewise,  the 
mixing  platform  or  machine  should  be  roofed  over.  It  is 
.  well,  also,  to  wet  down  the  finished  concrete  work  with  a 
hose  several  times  a  day  in  extremely  hot  weather,  and  less 
frequently  in  moderate  temperatures. 

58.  Concreting  in  Freezing  Weather. — While  it 
is  entirely  practicable  to  mix  and  place  concrete  at  a  temper¬ 
ature  as  low  as  27°  F.,  it  is  not  advisable  to  lay  concrete 
work  when  the  temperature  is  below  32°;  neither  should  it 
be  mixed  and  placed  even  at  this  temperature,  if  there  is  a 
possibility  that  the  temperature  will  fall.  If  concrete  is 
frozen,  its  setting  is  retarded  and  it  is  liable  to  become  worth¬ 
less,  never  properly  setting  and  obtaining  the  requisite  hard¬ 
ness  and  strength.  There  is,  however,  no  certainty  of  the 
action  of  frost  on  concrete,  as  frozen  concrete  will  frequently 
thaw  out  and  set,  with  apparently  little  loss  of  strength. 

59.  It  is  not  so  important  to  guard  against  freezing  in 
the  construction  of  large  masses  of  concrete,  such  as  would 
be  used  for  foundations  or  retaining  walls,  as  it  is  in  the 
construction  of  reinforced-concrete  work.  In  the  first  case, 


38 


PLAIN  CONCRETE 


§30 


the  concrete  is  protected  to  some  extent  by  its  mass.  In  the 
latter  construction,  however,  it  is  used  in  comparatively  small 
masses,'  and  as  there  must  be  no  uncertainty  regarding  its 
strength  in  compression  and  shear,  every  precaution  should 
be  taken  to  guard  against  freezing. 

Frozen  concrete  is  especially  dangerous  in  the  construction 
of  reinforced-concrete  buildings,  because  it  too  often  possesses 
the  apparent  solidity  and  hardness  of  concrete  that  has 
properly  set,  and  its  defectiveness  is  only  apparent  on  the 
removal  of  the  forms  and  the  subsequent  thawing  out  of  the 
concrete.  No  concrete  work  that  is  to  have  a  face  finish 
should  be  placed  in  freezing  weather,  as  frost  will  affect  the 
surface,  causing  exfoliation,  spalling,  pitting,  and  discoloration. 

60.  To  prevent  the  freezing  of  concrete  when  the  temper¬ 
ature  has  fallen  below  32°,  salt  is  sometimes  used  in  the  mix¬ 
ture.  The  addition  of  1J  pounds  of  salt  to  the  water  used 
with  1  bag  of  cement  will  not  decrease  the  strength  of  the 
concrete;  or,  a  10-per-cent,  solution  of  salt  can  be  used  in  the 
water  employed  in  mixing  the  concrete.  The  addition  of 
salt,  however,  is  never  advisable  if  a  surface  finish  is  required, 
as  it  is  liable  to  cause  efflorescence,  or  a  white  deposit,  on 
the  surface,  causing  the  work  to  become  very  unsightly. 

Concrete  should  never  be  made  from  ingredients  that  have 
been  subjected  to  freezing  weather  for  some  time  without  first 
thawing  them  out.  Aggregates  that  are  coated  with  ice  or 
that  have  been  exposed  to  severe  weather  for  a  long  time,  as 
well  as  the  sand  used  in  the  mixture  of  the  concrete,  should 
be  heated  or  thawed  out  before  being  used.  It  frequently 
happens  that  the  concrete  will  be  mixed  and  placed  during 
the  daytime,  when  the  temperature  is  near  32°  F.,  and  then 
left  to  set  during  the  night,  when  the  temperature  will  drop 
from  5°  to  10°.  Concrete  that  is  exposed  to  such  conditions 
should  always  be  protected  by  placing  over  it  a  layer  of  boards 
and  straw,  or  salt  hay,  or  cement  bags;  or,  where  the  work 
is  in  the  nature  of  a  reinforced-concrete  floor  system,  by 
heating  the  interior  of  the  structure  by  means  of  salamanders 
or  fires,  or  in  some  other  convenient  way. 


§30 


PLAIN  CONCRETE 


39 


61.  Joining  of  Old  Concrete  With  New. — New 

and  old  concrete  can  be  joined  only  with  difficulty,  and  the 
strength  of  such  a  connection  is  always  uncertain.  It  is  only 
with  the  greatest  care  that  a  cement-finished  coat  can  be 
made  to  adhere  to  a  concrete  base  that  has  reached  its  final 
set.  The  joining  of  old  and  new  concrete  work  is  best  done 
by  thoroughly  chipping,  or  cutting  away,  the  old  surface, 
saturating  it  with  water,  and  working  into  it  thin  coats  of  a 
1-1  Portland-cement  mortar,  and,  then,  while  the  coating  is 
still  fresh,  placing  against  it  the  new  concrete. 

There  are  some  high-grade,  imported  cements  that,  in  the 
form  of  cement  mortar,  more  readily  adhere  to  old  concrete 
work  than  the  usual  Portland  cements.  These  cements  are 
frequently  used  for  patching  and  piecing  out  work  already 
in  place. 

There  are  also  several  compounds  on  the  market  that  are 
assumed  to  possess  the  quality  of  joining  old  concrete  with 
the  new  in  a  manner  to  give  a  strength  equal  to  the  mass  of 
the  concrete.  These  compounds,  however,  have  been  used 
with  doubtful  success.  Comparative  tests  that  have  been 
made  where  such  compounds  have  been  used,  and  where 
junctions  have  been  carefully  made  with  new  concrete,  prove 
in  most  instances  that  they  have  little  efficiency. 

62.  Waterproofing  of  Concrete. — Plain  concrete  can 
.  be  rendered  nearly  waterproof  by  making  a  very  rich  mixture 
of  cement  mortar.  Such  a  mixture,  when  carefully  manip¬ 
ulated,  will  develop  waterproof  qualities.  Generally,  a 
concrete  composed  of  1  part  of  cement  and  1  part  of  sand, 
used  in  the  proportion  of  from  40  to  45  per  cent,  of  the  volume 
of  the  concrete,  will  be  impermeable  to  water. 

The  waterproofing  of  concrete  is  necessary  in  the  construction 
of  walls  below  grade,  and  also  in  building  bridge  arches, 
where  surface  water  is  likely  to  penetrate  the  filling  and  soak 
through  the  arch  construction,  badly  marking  the  surfaces  by 
causing  efflorescence.  For  constructions  like  these  a  wet 
mixture  of  concrete  containing  a  large  proportion  of  cement 
is  generally  used.  Such  a  mixture  is  not  usually  sufficient. 


40 


PLAIN  CONCRETE 


§30 


however,  to  insure  waterproof  walls  or  casings  for  retaining 
water,  such  as  tanks,  dams,  and  reservoirs.  Frequently, 
these  are  plastered  on  the  face  of  the  concrete  with  a  rich 
cement  mortar.  In  placing  this  mortar,  the  concrete  should 
be  well  wetted  and  the  surfaces  painted  with  a  coating  of 
neat  cement;  then  the  plaster  should  be  applied  in  layers  not 
over  \  inch  in  thickness,  the  coats  of  plaster  being  put  on  at 
intervals  of  about  an  hour. 

63.  A  superior  method  to  that  just  described  would  be 
to  form  the  concrete  mass  work  and  the  cement  face  work 
at  the  same  time.  This  can  be  done  by  placing  a  rich  cement 
mortar  between  the.  concrete  and  the  face  of  the  forms,  by 
plastering  the  faces  of  the  forms,  or  by  using  a  .sheet-iron 
slide,  which  is  raised  as  the  work  proceeds.  These  methods 
insure  a  waterproof  cement  coating  over  the  concrete  of  such 
a  thickness  and  so  incorporated  with  the  concrete  as  to  pre¬ 
clude  any  possibility  of  its  failing. 

In  another  method  that  has  been  successfully  used  for 
some  very  large  work,  concrete  is  rendered  waterproof  by 
the  use  of  soap  and  alum.  In  this  method,  a  waterproof 
mortar  is  made  by  using  1  part  of  Portland  cement  and 
2  parts  of  sand  to  which  f  pound  of  powdered  alum  has  been 
added  for  each  cubic  foot.  The  cement,  sand,  and  alum  are 
first  mixed  dry,  and  then  with  the  proper  quantity  of  water 
in  which  f  pound  of  soft  soap  has  been  dissolved  for  each 
gallon  of  water  used.  The  mortar  is  thoroughly  mixed  and 
is  applied  to  the  concrete  as  a  plaster,  to  the  thickness  of 
about  1  inch. 

64.  In  several  instances  where  a  plaster  coat  of  cement 
has  proved  ineffectual,  the  surface  has  been  made  waterproof 
by  applying  three  or  four  coats  of  a  solution  of  Castile  soap 
and  one  coat  of  a  solution  of  alum.  This  method  effectually 
stopped  the  leakage  of  a  concrete  stand  pipe  under  a  100-foot 
head  of  water. 

From  experience,  it  has  been  found  that  the  addition  of  a 
small  quantity  of  slaked  lime  to  a  concrete  mixture  will  tend 
to  make  it  waterproof;  but,  while  such  an  addition  does  not 


§30 


PLAIN  CONCRETE 


41 


materially  decrease  the  strength  of  concrete,  it  does  tend  to 
retard  the  setting.  Slaked  lime  added  to  concrete  crystallizes 
in  the  pores  of  the  material  and  in  this  way  makes  it  water¬ 
proof. 

Attempts  have  been  made  to  make  concrete  waterproof  by 
mixing  various  chemicals  with  it.  Among  others,  silicate  of 
soda,  commonly  known  as  water  glass,  has  been  used.  This 
material,  however,  tends  to  decrease  the  strength  of  the  con¬ 
crete — in  some  instances  as  much  as  50  per  cent. 

An  effectual  method  of  waterproofing  concrete  is  to  apply 
hot  pitch  to  the  surface  to  be  waterproofed.  The  pitch, 
however,  must  be  very  thin,  and  can  only  be  applied  as  a 
thin  coating,  as  it  is  not  easy  to  make  the  pitch  adhere  in 
any  thickness  to  a  vertical  surface. 

There  are  several  concrete  waterproofing  compounds  on 
the  market.  These  have  been  successfully  used  in  a  number 
of  instances  for  the  construction  of  waterproof  roof  -slabs, 
cisterns,  tunnels,  walls,  and  other  work  of  this  character. 


BUILDING  STONE  AND  BRICK 


STONE 


PHYSICAL  PROPERTIES  OF  BUILDING  STONE 

1.  In  order  to  be  able  to  decide  which  kind  of  stone  is 
best  to  use  under  given  conditions,  a  knowledge  of  the 
different  kinds  employed  in  building  construction  is  very 
essential.  It  is  not  necessary  for  a  builder  to  determine  the 
exact  composition  of  a  stone,  but  his  knowledge  should  be 
sufficient  to  aid  him  in  selecting  or  specifying  the  kind  of 
stone  best  adapted  to  the  purposes  for  which  it  is  intended. 

The  structural  manner  in  which  the  constituent  parts  of  * 
the  rocks  are  grouped  together  bears  a  greater  relation  to 
the  value  or  quality  of  the  rock  than  the  character  of  the 
minerals  composing  it;  or,  in  other  wTords,  the  physical  char¬ 
acteristics  may  be,  and  frequently  are,  more  important  than 
the  chemical  qualities. 

2.  Density. — The  weight,  strength,  and  absorptive 
properties  of  stone  are  dependent  on  the  density.  Thus, 
among  rocks  having  the  same  mineral  composition  but  dif¬ 
fering  as  to  structure,  generally  the  strongest  will  be  the 
densest  and  the  heaviest  will  be  the  least  absorptive. 

3.  Hardness. — The  manner  in  which  the  mineral  con¬ 
stituents  of  a  rock  are  cemented  to  each  other  and  the 
individual  hardness  of  such  mineral  constituents  determine 
the  hardness  of  the  rock  as  a  structure.  The  minerals 
composing  a  rock  may  be  hard,  but  the  rock  itself  as  a 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS*  HALL,  LONDON 

i  31 


2 


BUILDING  STONE  AND  BRICK 


§31 


structure  will  be  soft  if  the  particles  do  not  strongly  adhere 
to  one  another.  Thus,  some  of  the  softest  sandstones  are 
composed  of  quartz,  which  is  a  hard  mineral,  but  the  grains 
are  so  weakly  cemented  together  that  the  stone  as  a  whole 
is  soft. 

4.  Structure. — The  structure  of  a  rock  depends  on 
the  form,  size,  and  arrangement  of  its  component  minerals. 
All  rocks  may  be  approximately  classified  as  crystalline , 
vitreous  or  glassy,  and  fragmental.  Granite  and  crystalline 
limestone  may  be  taken  as  types  of  the  crystalline  group; 
obsidian  and  pitchstone  may  be  taken  as  types  of  the  vitre¬ 
ous  group;  while  the  sandstones  are  types  of  the  fragmental 
group. 

5.  Though  all  rocks  have  some  common  structural  char¬ 
acteristics,  certain  peculiarities  are  found  only  in  single 
types  of  rock.  If  the  structure  can  be  recognized  by  the 
unaided  eye,  the  rock  is  said  to  have  a  macroscopic  structure , 
and  such  rocks  may  then  be  described  as  being  either 
granular,  massive,  stratified,  schistose,  porphyritic,  or  con¬ 
cretionary. 

The  term  granular,  as  its  name  implies,  is  applied  to  rocks 
built  up  of  distinct  grains  of  crystalline,  fragmental,  or  water- 
worn  character. 

The  term  massive ,  or  unstratified ,  is  applied  to  rocks  that 
are  not  arranged  in  any  definite  form  in  layers,  or  strata,  but 
have  the  constituent  parts  mingled  together,  as  in  diabase 
and  granite. 

The  term  stratified  is  applied  to  rocks  composed  of  par¬ 
allel  layers,  or  beds,  as  is  frequently  seen  in  limestone  and 
sandstone. 

The  term  schistose  is  applied  to  stratified  crystalline  rocks 
that  are  in  comparatively  thin  scaly  layers. 

The  term  porphyritic  is  applied  to  rocks  that  consist  of  a 
ground  mass  of  fine  or  compact  and  evenly  crystallized 
material,  with  larger  crystals  of  feldspar  scattered  through 
it.  A  granite  fragment  has  a  porphyritic  structure,  but  it  is 
difficult  to  distinguish  owing  to  the  similarity  of  color  exist- 


§31 


BUILDING  STONE  AND  BRICK 


3 


ing  between  the  crystals  and  the  ground  mass.  In  such  rocks 
as  the  felsites,  it  is  quite  noticeable.  In  the  porphyries  of 
Eastern  Massachusetts,  the  ground  mass  is  of  a  black  or 
neutral  color  and  very  compact  and  dense,  while  the  large 
white  crystal  feldspars  are  in  marked  contrast.  The  porphy- 
ritic  structure  is  so  noticeable  that  any  rocks  possessing  this 
characteristic  in  a  marked  degree  are  commonly  termed 
porphyries ,  without  regard  to  the  mineral  composition.  The 
word  porphyry  is  now  commonly  applied  as  an  adjective, 
because  any  rock  may  possess  this  structure,  whatever  may 
be  its  origin  or  composition. 

The  term  coyicret ionary  is  applied  to  rocks  composed  of 
concretions,  or  rounded  particles  built  up  by  the  collections 
of  mineral  matter  around  a  center,  forming  a  rounded  mass 
of  concentric  layers  like  the  coating  of  an  onion.  When  the 
concretions  are  small,  like  the  roe  of  a  fish,  the  structure  is 
called  oolitic;  when  large,  like  a  pea,  the  structure  is  called 
pisolitic.  The  Bedford,  Indiana,  limestones  are  examples  of 
the  oolitic  type.  The  concretionary  structure  is  rarely  found 
in  crystalline  rocks. 

6.  Aggregation  of  Particles. — The  hardness  of  rock 
depends  largely  on  the  aggregation  of  the  particles; 
therefore,  the  working  qualities  of  the  rock  are  fixed  by  the 
character  of  this  aggregation.  If  the  grains  are  loosely 
coherent  in  a  rock  composed  of  hard  minerals,  it  may  be 
worked  readily,  while  a  rock  consisting  of  softer  materials 
may  be  worked  with  difficulty  because  the  particles  tenaciously 
cohere  to  each  other. 

The  durability  of  a  stone  is,  to  a  great  extent,  a  matter  of 
texture.  If  the  grains  cohere  closely,  the  stone  will  be  less 
absorbent  and  more  durable  than  one  in  which  the  cohesion 
is  not  so  great,  as  in  the  friable  and  loose-textured  rocks. 

The  kind  of  fracture  shown  by  a  rock  is  determined  by  the 
fineness  or  the  coarseness  of  the  grain  and  the  relation  of 
the  particles  to  themselves  or  their  state  of  aggregation. 
Such  rocks  as  flint,  obsidian,  and  some  varieties  of  lime¬ 
stone  have  a  compact,  fine  grain,  show  a  concave  or  convex 


4 


BUILDING  STONE  AND  BRICK 


31 


shell-like  face  of  conchoidal  form  on  fracture,  and  are  difficult 
to  dress.  Other  stones  show,  on  fracture,  a  jagged  surface  or 
split  along  certain  planes,  all  dependent  on  the  aggregation 
of  the  particles. 

7.  Rift  and  Grain. — The  rift  of  a  rock  is  a  line  of 
cleavage  parallel  to  the  bed  and  is  visible  in  such  rocks  as 
mica  schist,  gneiss,  and  other  sedimentary  rocks.  It  is  along 
these  lines  that  the  rock  can  be  readily  split.  Rift,  however, 
is  commonly  found  in  massive  rocks,  although  it  is  not  so 
easily  discerned  as  in  the  examples  cited.  The  grain  of  a 
rock  is  always  at  right  angles  to  the  plane  of  the  rift  or  the 
bed. 

Rocks  that  do  not  possess  rift  and  grain  cannot  be  worked 
into  rectangular  form  without  great  difficulty,  unless  they 
are  of  a  very  soft  nature,  but  with  rift  the  hardest  rocks  can 
be  readily  worked;  for  instance,  the  South  Dakota  quartzite, 
which  is  one  of  the  hardest  rocks  known,  can  be  broken  into 
pieces  for  paving  as  easily  as  can  a  soft  sandstone  or  a 
granite. 

8.  Color.  The  chemical  properties  of  a  rock,  as  a  rule, 
determine  its  color.  The  color  of  granites,  however,  is 
affected  by  the  action  of  light  on  the  feldspars,  which  when 
clear  and  glassy,  absorb  the  light,  making  the  rock  apparently 
darker  than  when  the  feldspars  are  white  and  opaque  and 
reflect  the  light. 

Iron,  the  principal  coloring  matter  in  rocks,  may  be  found 
in  chemical  composition  with  other  minerals  or  in  such  sim¬ 
pler  compounds  as  the  sulphides  and  carbonates,  or  as  an 
oxide  distributed  throughout  the  mass  of  rock.  The  brownish 
or  reddish  hues  are  due  to  the  free  oxides  of  iron,  while  the 
bluish  or  grayish  hues  are  caused  by  the  carbonates  or  the 
sulphides.  The  absence  of  iron  in  any  of  its  forms  is  usually 
indicated  by  the  white,  or  nearly  white,  color  of  the  rock. 
The  permanency  of  the  color  of  the  rock  depends  on  the 
form  in  which  the  iron  is  found.  Oxidation  is  likely  to  result 
if  it  is  in  the  form  of  a  sulphide,  carbonate,  or  other  protoxide 
compound.  Therefore,  stone  containing  these  forms  of 


§31 


BUILDING  STONE  AND  BRICK 


5 


iron  is  likely  to  fade  and  turn  yellowish  and  stain  on  expo¬ 
sure.  The  sesquioxide,  being  in  the  last  stages  of  oxidation, 
can  undergo  no  further  change  and  is  therefore  a  permanent 
color;  hence,  the  decidedly  red  color  may  be  considered  as 
permanent.  The  blue  and  the  black  colors  of  marbles  and 
limestones  are  largely  caused  by  the  presence  of  carbonaceous 
matter,  usually  of  vegetable  origin. 


CLASSIFICATION  OF  BUILDING  STONE 

9.  Building  stones  are  usually  classified  according  to 
their  geological  formation  or  their  chemical  composition. 
The  classification  given  here,  however,  is  strictly  in  relation 
to  their  use  in  building,  and  includes  the  following  groups: 
the  granitic ,  the  sandstone,  the  slate,  and  the  limestone. 


GRANITIC  GROUP 

10.  The  granitic  group  of  rocks  is  richest  in  silica 
and  therefore  its  members  are  known  as  silicious  stones.  In 
this  group  are  included  granite,  syenite,  gneiss,  greenstone, 
and  trap. 

11.  Granite. — The  granites  are  unstratified  and  under¬ 
lie  the  stratified  rocks.  They  are  composed  of  an  aggrega¬ 
tion,  or  assemblage,  of  crystals  of  feldspar,  quartz,  and  mica, 
the  principal  impurities  being  hornblende  and  talc.  The 
colors  of  granite  are  white,  grayish  white,  yellowish,  reddish, 
rose,  flesh  color,  or  deep  red,  but  rarely  green.  Granite  is 
distinguished  by  its  even  and  brilliant  fracture,  •  its  pearly 
luster,  and  its  outline,  which  is  seldom  regular,  but  in  which 
may  be  recognized  rectangles  and  parallelograms. 

Granite  varies  in  quality  according  to  the  proportions  of 
its  components  and  their  method  of  aggregation.  Stone  of 
the  greatest  durability  and  hardness  contains  a  greater  pro¬ 
portion  of  quartz  and  a  smaller  proportion  of  feldspar  and 
mica.  Hornblende  renders  the  stone  tough  and  heavy. 
Feldspar  renders  it  lighter  in  color,  easier  to  cut,  and  more 


6 


BUILDING  STONE  AND  BRICK 


§31 


susceptible  to  decomposition  by  the  solution  of  potash  con¬ 
tained  in  it.  Mica  renders  it  friable. 

The  durability  of  granite  depends  on  the  quantity  of  quartz 
present  and  on  the  nature  of  the  feldspar.  Potash  feldspar 
is  less  durable  than  lime  or  soda  feldspar.  Mica,  being 
easily  decomposed,  is  an  element  of  weakness.  An  excess 
of  lime  or  soda  in  the  mica  or  feldspar  hastens  disintegra¬ 
tion,  as  does  also  an  excess  of  iron.  Stones  showing  large 
and  dark  iron  stains  should  be  rejected  for  outside  work. 
Fine-grained  granite  weathers  better  than  does  granite  of 
coarser  grain.  When  mica  predominates,  granite  passes 
into  gneiss. 

The  granites  are  among  the  most  valuable  of  the  building 
stones  and  are  extensively  used  in  important  works.  They 
can  be  readily  quarried  and  by  reason  of  the  lack  of  grain  in 
the  stone,  blocks  can  be  obtained  of  any  size.  On  account 
of  its  great  hardness,  granite  is  difficult  to  work  and  there¬ 
fore  very  costly  to  use  if  the  stone  has  to  be  cut.  It  weighs 
about  166  pounds  per  cubic  foot. 

Granite  is  found  in  the  eastern  part  of  the  United  States, 
in  Canada,  in  many  parts  of  the  Rocky  Mountains,  and,  as  a 
rule,  wherever  the  later  rock  formations  and  the  underlying 
beds  have  been  left  exposed.  It  is  generally  classified  into 
gray  and  red.  Gray  granite  is  found  throughout  New 
England,  the  border  states,  and  in  Virginia.  Red  granite  is 
composed  of  red  orthoclase  (aluminum  potassium  silicates), 
bluish  quartz,  and  a  little  hornblende,  with  very  little  mica. 
It  is  hard  and  takes  a  fine  polish.  It  is  found  near  the  Bay 
of  Fundy,  near  Lake  Superior,  on  the  islands  of  the 
St.  Lawrence  River,  in  Virginia,  Maine,  and  many  parts  of 
the  Rocky  Mountains. 

12.  Syenite. — The  stone  known  as  syenite  derives  its 
name  from  Syene,  in  Egypt.  It  consists  of  feldspar  and 
hornblende,  frequently  associated  with  mica  and  quartz;  is  of 
a  granular  texture,  closely  resembling  ordinary  granite,  but 
somewhat  darker;  and  is  hard  and  tough,  somewhat  coarse¬ 
grained,  and  will  not  take  a  polish.  It  is  one  of  the  most 


§31 


BUILDING  STONE  AND  BRICK 


7 


durable  of  the  granitic  rocks  when  its  feldspar  constituent  is 
not  too  readily  decomposed  by  the  removal  of  the  potash 
when  exposed  to  the  weather.  For  this  reason,  it  should  be 
carefully  tested  before  it  is  used. 

13.  Gneiss  and  Mica  Slate. — In  composition,  gneiss 
and  mica  slate  are  similar  to  granite,  but  they  differ  from 
it  in  being  stratified.  Granite,  syenite,  and  gneiss  resemble 
one  another  so  closely  that  they  are  all  frequently  called 
granite  by  persons  not  familiar  with  their  characteristics. 

Gneiss  is  not  so  valuable  a  stone  as  granite  on  account  of 
its  stratification,  which  will  not  permit  it  to  be  split  evenly 
in  any  desired  direction.  Although  it  is  not  so  strong  as 
granite,  it  is  a  good  building  material  and  often  answers 
just  as  well. 

14.  Greenstone,  Trap,  and  Basalt. — The  igneous, 
unstratified  rocks,  known  as  greenstone,  trap,  and  basalt, 
consist  of  hornblende  and  feldspar.  The  term  trap  has  been 
suggested  as  a  generic  name  for  these  rocks.  The  green¬ 
stone  is  not  so  coarse-grained  as  granite,  and  in  the  trap  and 
basalt  the  granular  structure  is  not  apparent.  The  green¬ 
stone  and  trap  break  into  blocks,  and  the  basalt  into  columns 
of  prismatic  form.  They  are  found  in  veins  and  dikes  and 
injected  among  the  stratified  rock  of  all  ages. 

These  rocks  vary  in  color,  from  nearly  white  in  some 
varieties  of  greenstone,  to  nearly  black,  as  in  basalt,  the 
difference  in  color  being  determined  by  variation  in  the 
proportions  of  hornblende,  which  gives  a  dark  color,  and 
feldspar,  which  gives  a  light  color.  The  green  is  due  to 
chromium.  These  stones,  while  making  very  durable  build¬ 
ing  material,  cannot  be  obtained  in  large  blocks  and  are 
difficult  to  cut.  Trap  rock  forms  one  of  the  best  aggre¬ 
gates  for  use  in  making  concrete. 


SANDSTONE  GROUP 

15.  Such  material  as  sandstone  consists  of  fragmen¬ 
tary  rocks,  composed  mostly  of  grains  of  silica  (quartz), 
cemented  together  by  a  deposition  of  silica,  carbonate  of 
211—7 


8 


BUILDING  STONE  AND  BRICK 


31 


lime,  oxide  of  lime,  and  aluminous  matter.  Sandstone  is  a 
stratified  rock  and  belongs  to  the  later  geological  periods. 

If  the  cementing  material  is  silica,  the  rock  is  very 
durable,  but  difficult  to  work.  Iron  oxide  in  the  cementing 
material,  consisting  of  carbonate  of  lime  and  clayey  matter, 
gives  the  stone  a  reddish  or  brownish  color.  Lime  renders 
the  stone  particularly  liable  to  disintegration  when  exposed 
to  an  atmosphere  containing  gases,  or  when  used  for  founda¬ 
tions  in  a  soil  that  is  impregnated  with  acid  water.  The 
presence  of  clay  or  oxide  of  iron  is  also  deleterious. 

Sandstones  are  variable  in  character,  some  being  nearly 
as  valuable  as  granite  while  others  are  practically  useless  for 
permanent  construction.  The  best  stone  is  characterized  by 
small  grains  with  a  small  proportion  of  cementing  material, 
and  when  broken  has  a  bright,  clear,  sharp  fracture.  It  is 
usually  found  in  thick  beds  and  shows  slight  evidences  of 
stratification.  Water  can  readily  penetrate  between  the 
layers  of  this  stone;  therefore,  in  foundations  it  should  be 
laid  on  its  natural  bed  so  that  the  penetration  of  moisture 
and  possible  disintegration  by  freezing  may  be  prevented  as 
much  as  possible. 

Sandstone  of  good  quality  possesses  strength  and  dura¬ 
bility  and  can  be  readily  cut  and  dressed.  These  qualities 
make  it  one  of  the  most  frequently  used  of  the  common 
building  stones.  When  the  grains  are  extremely  small,  it  is 
termed  a  “freestone”  because  of  the  ease  with  which  it  can 
be  quarried,  cut,  and  dressed. 

When  quarried,  sandstones  are  usually  saturated  with 
quarry  water  and  are  very  soft;  but  on  exposure  to  the  air 
and  on  drying,  they  become  hard. 

Sandstones  vary  much  in  color.  The  Ohio  and  Nova 
Scotia  varieties  are  yellowish  and  cream  color  and  some¬ 
times  nearly  white;  the  Missouri  sandstone  is  of  a  yellowish- 
drab  color  and  possesses  durability;  the  Portland,  Connecticut; 
Newark,  New  Jersey;  Marquette,  Michigan;  and  Bass  Island, 
in  Lake  Superior,  sandstones  are  of  a  dark  brownish-red 
color,  which  is  due  to  the  presence  of  iron,  and  are  termed 
brow?istones.  The  Potsdam,  New  York,  red  sandstone  is 


§  31 


BUILDING  STONE  AND  BRICK 


9 


durable,  hard,  highly  silicious,  and  of  a  reddish  color.  The 
Hummelstown,  Pennsylvania,  sandstone  has  a  brownish 
color.  A  fine-grained  blue  sandstone  is  known  as  bluestone. 
This  variety  is  widely  used  for  trimmings  and  for  stone 
sidewalks,  as  it  readily  splits  into  slabs. 


SLATE  GROUP 

16.  Slate  is  a  stratified  rock  of  great  hardness  and 
density,  with  a  laminated  structure.  It  splits  readily  along 
planes  called  planes  of  slaty  cleavage.  This  facility  of  cleav¬ 
age  is  one  of  the  most  valuable  characteristics  of  slate,  as  it 
enables  masses  to  be  split  into  slabs  and  plates  of  small 
thickness  and  great  area. 

The  color  of  slates  varies  greatly;  those  most  frequently 
met  with  are  dark  blue,  bluish  black,  purple  gray,  bluish 
gray,  and  green.  Red  and  cream-colored  slates  are  also 
occasionally  found.  Some  slates  are  marked  with  bands  or 
patches  of  color  differing  from  the  general  color  of  the  stone. 
These  marks  are  generally  considered  not  to  injure  the  dura¬ 
bility  of  the  slate,  but  they  lower  its  quality  by  detracting 
from  its  appearance. 

Ribs ,  or  veins ,  are  dark  marks  running  through  some  slates. 
They  are  always  objectionable,  but  are  particularly  so  when 
they  run  in  the  direction  of  the  length  of  the  slate,  which  is 
very  liable  to  split  along  the  vein.  These  veins,  or  ribs,  are 
frequently  soft  and  of  inferior  quality  to  that  of  the  slate 
proper,  and  slates  containing  them  should  not  be  allowed  in 
good  work. 

Although  not  strictly  a  building  stone,  slate  is  used  exten¬ 
sively  for  covering  steps  and  the  roofs  of  buildings,  for  Wall 
linings,  and  for  sanitary  appliances. 


LIMESTONE  GROUP 

17.  All  limestones  are  of  sedimentary  origin  and  have 
for  their  principal  ingredient  carbonate  of  lime,  which  is 
combined  with  various  minerals.  The  presence  of  these 


10 


BUILDING  STONE  AND  BRICK 


§31 


minerals  gives  rise  to  the  division  of  the  limestones  into 
five  classes,  each  of  which  is  designated  by  the  name  of  the 
predominating  mineral.  When  clay  is  present,  the  stone  is 
called  argillaceous  limestoiie;  when  silica  predominates,  silicious 
limestone;  when  it  contains  iron,  ferruginous  li?nesto7ie;  and 
when  magnesia  is  present  to  the  extent  of  15  per  cent.,  mag¬ 
nesian  limestone.  When  the  carbonate  of  lime  and  the  car¬ 
bonate  of  magnesia  are  combined  in  equal  proportions,  the 
stone  is  called  dolomite.  Limestones  are  either  granular  or 
compact. 

18.  Granular  limestone  consists  of  carbonate  of  lime 
in  grains,  which  are  in  general  sea  shells  or  fragments  of 
shells  cemented  together  by  some  compound  of  lime,  silica, 
and  alumina,  and  often  mixed  with  a  greater  or  smaller 
quantity  of  sand.  Granular  limestone  is  always  more  or  less 
porous.  It  is  found  in  various  colors,  especially  white  and 
light  yellowish  brown.  In  many  cases,  it  is  so  soft  when 
first  quarried  that  it  can  be  cut  with  a  knife;  it  hardens, 
however,  on  exposure  to  the  air.  The  variety  of  granular 
limestone  called  oolitic ,  from  the  appearance  of  the  stone, 
which  is  that  of  egg-shaped  grains  cemented  together,  is 
one  of  the  most  important  of  the  limestone  group,  and  is 
extensively  quarried  and  widely  used  for  building  purposes. 
Each  grain  is  usually  of  concentric  structure,  the  carbonate 
of  lime  enclosing  a  particle  of  sand  or  some  substance  of 
either  animal  or  vegetable  origin. 

19.  Compact  limestone  consists  of  carbonate  of  lime, 
either  pure  or  mixed  with  sand  or  clay.  This  kind  of  lime¬ 
stone  is  generally  devoid  of  crystalline  structure,  and  has  a 
dull,  earthy  appearance  and  a  dark-blue,  gray,  black,  or 
mottled  color.  In  some  cases,  however,  it  is  crystalline  and 
full  of  organic  remains;  it  is  then  known  as  crystalline  limestone . 

The  compact  limestones  are  easily  worked  with  the  saw 
and  hammer,  resemble  light  granite  in  appearance,  and  are 
extensively  used  for  building  purposes.  The  variety  called 
shelly  limestone  consists  of  fossil  shells  that  are  cemented 
together  and  is  sufficiently  hard  to  take  a  polish;  it  is  much 


§31 


BUILDING  STONE  AND  BRICK 


11 


used  for  interior  ornamentation.  The  condition  of  the 
minerals  combined  with  the  lime  also  furnishes  a  basis  for 
distinguishing  names.  The  stone  is  called  hornstone  when 
very  fine-grained  silica  is  present;  clierty ,  when  the  silica  is 
in  the  form  of  rounded  masses  or  nodules;  ironstone ,  when 
the  amount  of  iron  and  clay  is  greater  than  the  amount  of 
lime;  rottenstone,  when  the  ironstone  is  decomposed;  hydraulic 
limestone ,  when  the  rock  is  composed  of  lime,  silica,  and  clay 
in  nearly  equal  proportions. 

20.  The  limestones  form  an  important  and  useful  group 
of  stones,  but  not  all  are  suitable  for  structural  purposes; 
some  are  too  friable,  and  others  too  brittle.  The  compact 
and  granular  varieties,  however,  are  generally  suitable  for 
masonry.  Their  durability  depends  mainly  on  the  texture; 
when  this  is  compact,  the  stone  is  very  durable,  except  when 
exposed  to  the  acid  vapors  of  cities.  Nearly  all  the  varieties 
are  attacked  by  sulphuric  acid,  which  forms  a  soluble  sulphate 
of  magnesia  that  may  be  easily  washed  away. 

21.  Marble. — Metamorphosed  limestone  gives  the 
masonry  material  known  as  marble,  which  is  easily  dressed 
to  a  smooth  surface  and  polished.  For  building  purposes, 
the  granular  varieties  are  generally  superior  to  the  compact. 
The  impure  carbonates  of  lime  are  sometimes  of  great  value 
as  marble.  The  magnesian  limestones,  or  the  dolomites, 
are  usually  of  excellent  quality. 

White  marble  is  found  in  the  Laurentian  rocks,  Canada, 
but  much  of  that  used  in  the  Northern  Atlantic  States  is 
obtained  from  the  Green  Mountains,  which  extend  through 
Vermont,  Western  Massachusetts,  Western  Connecticut,  and 
Southeastern  New  York.  Quarries  exist  at  Granden,  Rutland, 
Danby,  Dorset,  and  Manchester,  in  Vermont;  at  Lanesborough, 
Lee,  Stockbridge,  Great  Barrington,  and  Sheffield,  in  Mas¬ 
sachusetts;  at  Canaan,  in  Connecticut;  and  at  Pleasantville 
and  Tuckahoe,  in  New  York.  The  snowflake  variety  of 
marble  is  obtained  from  the  Pleasantville  quarries,  and  a  fine 
grade  of  statuary  marble  is  from  Rutland,  Vermont.  From 
this  place  southward,  the  marbles  become  coarser  and  harder 


12 


BUILDING  STONE  AND  BRICK 


§31 


and  more  suitable  for  building  purposes.  Dolomitic  marbles 
are  found  in  the  southeastern  part  of  New  York  and  in 
Delaware.  White  dolomite  marble  is  found  in  Maryland. 

.  The  colored  marbles  used  in  building  construction  are  of 
several  varieties  and  are  found  in  Vermont,  Connecticut, 
New  York,  Pennsylvania,  and  Tennessee.  Brecciated  marbles , 
that  is,  those  in  which  the  conglomerate  fragments  are 
angular  instead  of  water-worn,  are  found  in  Vermont  on  the 
shores  of  Lake  Champlain,  and  a  dove-colored  marble  with 
greenish  veins  is  found  at  Rutland.  Black  marbles  are 
found  at  Shoreham,  Connecticut,  and  Williamsport,  Pennsyl¬ 
vania.  Black  Trenton  limestone  is  found  at  Glens  Falls,  New 
York.  The  Warwick  marble,  found  in  Orange  County,  New 
York,  is  beautifully  colored  with  carmine,  with  white  veins. 
The  Knoxville  marble  is  of  a  reddish-brown  color  with  lines 
of  blue.  Tennessee  marble  is  brown  and  white  mottled. 
The  foreign  marbles  are  largely  imported  from  Italy,  Spain, 
and  Belgium.  The  Bardiglio,  of  Italy,  is  of  a  gray  color 
shaded  with  black;  the  Siena,  of  Spain,  is  a  pale  yellow 
Color;  the  Lisbon,  of  Portugal,  a  pale  reddish  color;  and  the 
Belgian,  of  Belgium,  is  black.  Verde  antique  is  composed 
of  bands  of  serpentine  and  white  marble. 

22.  Chalk. — Soft  limestone  in  which  the  minute  shells 
composing  it  have  not  been  entirely  destroyed  by  the  pres¬ 
sure  to  which  it  has  been  subjected  in  early  geological  times 
is  called  chalk.  It  is  not  suitable  for  constructive  purposes, 
but  is  very  useful  in  making  lime  and  cement. 

23.  Quicklime. — The  material  known  as  quicklime 
is  obtained  by  calculation  from  various  limestones  and  is  the 
basis  of  common  mortar;  the  act,  or  operation,  of  calcination 
is  the  expelling,  by  heat,  of  carbon  dioxide  by  which  the 
stone  is  broken  down  and  reduced  to  the  oxide  state. 

24.  Plaster  of  Paris. — The  material  known  as  gypsum, 
alabaster,  or  plaster  of  Paris  is  a  sulphate  of  lime  con¬ 
taining  water  of  crystallization.  The  term  “plaster  of  Paris” 
is  due  to  the  fact  that  large  deposits  of  this  stone  underlie 
the  city  of  Paris.  This  natural  sulphate  of  lime,  when  raised 


§31 


BUILDING  STONE  AND  BRICK 


13 


to  a  high  temperature,  loses  its  water  of  crystallization  and  is 
then  ground  into  a  fine  powder.  This  becomes  the  plaster 
of  Paris  of  commerce,  which  is  used  for  molds,  ornaments, 
and  casts,  as  well  as  in  wall  plaster  and  staff.  Gypsum  is 
found  in  many  parts  of  the  United  States,  great  quantities 
coming  from  the  state  of  New  York. 


FIRE-STONES 

25.  Fire-stones  are  stones  capable  of  resisting  the 
action  of  great  heat  without  fusing,  exfoliating,  or  cracking. 
Lime  and  magnesia,  except  in  the  form'  of  silicates,  are 
prejudicial  to  the  quality  of  fire-stones;  potash,  also,  is  very 
injurious  because  it  increases  the  fusibility  of  the  stone, 
which,  on  melting,  causes  the  formation  of  a  fusible  glass. 
Quartz  and  mica  alone  or  in  combination  make  the  most 
refractory  stones.  Mica,  slate,  and  gneiss  make  an  excellent 
combination.  Gneiss  is  particularly  refractory  when  it  con¬ 
tains  a  considerable  portion  of  arenaceous  quartz;  that  is, 
quartz  in  which  the  particles  partake  of  the  nature  of  sand. 

Limestones  do  not  stand  well  in  the  presence  of  high  tem¬ 
peratures,  as  they  sometimes  explode,  owing  to  the  rapid 
expulsion  of  the  carbonic-acid  gas. 

Granitic  and  other  primary  rocks  usually  contain  some 
water,  which,  in  the  presence  of  fire,  causes  them  to  crack  and 
sometimes  explode. 

Sandstones,  if  somewhat  porous,  uncrystallized,  and  free 
from  feldspar,  are  the  most  refractory  of  the  common  build¬ 
ing  stones. 

Firebrick  is  perhaps  the  most  fire-resisting  building 
material  now  known,  while  common  hard-burned  brick  is 
more  refractory  than  any  of  the  building  stones. 

Concrete  made  of  Portland  cement  is  a  fire-resisting 
medium  of  value. 


14 


BUILDING  STONE  AND  BRICK 


§31 


DURABILITY  OF  BUILDING  STONE 

26.  In  the  structural  use  of  building  stones,  it  is  seldom 
that  the  full  safe  strength  of  the  stone  is  required  to  resist 
the  stresses  imposed,  and  consequently  the  range  of  choice 
is  not  limited  by  this  consideration  so  much  as  by  the  factor 
of  durability .  While  in  architectural  work  color  is  of  great 
importance,  for  on  it  the  architect  depends  to  a  large  extent  for 
the  success  of  his  design,  it  is  exceptional  in  purely  structural 
work  for  the  color  of  the  stone  to  be  a  deciding  factor. 

The  durability  of  a  building  stone  depends  not  only  on 
the  physical  and  chemical  formation  of  the  stone,  but  to  a 
considerable  extent  on  the  climate  in  which  the  structure  is 
to  be  built  and  also  the  method  employed  in  quarrying  the 
material.  Where  a  selection  is  to  be  made  of  two  stones 
equally  durable  and  structurally  fit  for  their  purpose,  the 
economic  consideration  influences  the  choice.  The  cost  of 
structural  building  stones  is  regulated  by  the  difficulties  of 
quarrying,  the  refractory  nature  of  the  stone  in  finishing,  and 
the  distance  it  must  be  transported. 

27.  Physical  Structure. — The  most  durable  building 
stones  are  generally  of  a  compact  and  uniform  texture  and 
show  a  clean  fracture  free  from  earthy  or  soluble  mineral 
matter.  Stones  showing  lamination,  or  layers,  are  not  likely 
to  prove  as  durable  as  those  of  a  more  homogeneous  struc¬ 
ture,  especially  when  laid  with  the  laminations  on  edge ,  or 
perpendicular  to  the  bed  of  the  wall. 

Non-porosity  is  not  always,  a  quality  synonymous  with 
durability,  because  many  stones  that  absorb  moisture  also 
permit  of  its  rapid  evaporation.  Such  stones  are  likely  to 
prove  more  durable  than  those  which  absorb  less  moisture 
and  part  with  it  more  reluctantly. 

Stones  showing  a  streaked  appearance  and  lack  of  uniform¬ 
ity  in  color  are  usually  composed  of  several  minerals  of 
various  degrees  of  hardness,  and  in  some  instances  one  of 
them  may  be  slightly  soluble.  Such  stones  are  not  likely  to 
weather  well,  because  the  softer  or  more  soluble  mineral  will 


§31 


BUILDING  STONE  AND  BRICK 


15 


be  corroded  and  washed  away,  leaving  the  harder  substance 
to  protrude.  When  the  less  durable  substance  is  in  small 
pockets,  or  spots,  the  stone  will,  on  long  exposure,  be  pitted; 
while  if  the  softer  mineral  is  in  streaks,  or  veins,  the  material 
will  be  grooved,  fissured,  or  channeled. 

Small  fossils  or  shells  embedded  in  the  substance  of  a 
building  stone  have  usually  a  deleterious  influence  on  its 
durability  and  weathering  qualities.  Such  fossils  and  shells 
are  calcareous  in  nature  and  generally  soft  and  partly  soluble 
under  atmospheric  influences.. 

28.  Climate  and  Environment. — Building  stones  of 
the  most  durable  character  are  required  in  climates  where 
the  changes  in  temperature  are  great  and  where  there 
is  much  moisture  in  the  atmosphere.  The  structure  of  a 
stone  consists  of  minute  particles  that  are  surrounded  by  a 
matrix  that  forms  the  cementing  material  of  the  mass  or  are 
closely  attached  to  each  other  by  cohesion.  In  either  case, 
changes  in  temperature  cause  these  particles  to  expand  and 
contract  with  considerable  force,  thus  loosening  particles 
from  the  matrix  or  from  each  other  and  causing  deteriora¬ 
tion  and  the  ultimate  destruction  of  the  rock.  The  freezing 
of  water  in  the  pores  of  the  stone  or  in  the  crevices  and  the 
spaces  between  the  laminatibns  in  stratified  stones,  is  the 
primary  cause  of  the  rapid  destruction  of  some  building 
stones.  Water  in  freezing  expands  about  one-tenth  of  its 
bulk  and  is  said  to  be  capable  of  exerting  a  pressure  of  about 
150  tons  per  square  foot,  which  is  sufficient,  under  favorable 
conditions,  to  split  the  strongest  rocks.  The  freezing  of 
moisture  within  the  pores  of  the  stone  is  very  deleterious 
to  the  stability  of  its  structure,  especially  if  there  is  not 
contained  in  the  rock  sufficient  reserve  pore  space  to  accom¬ 
modate  the  increased  bulk  of  the  water  when  frozen.  Some¬ 
times,  clay  is  one  of  the  constituents  of  sandstone.  When 
acted  on  by  the  frost,  the  clay  will  swell  by  reason  of  the 
water  contained  in  it,  and  the  stone  will  begin  to  disintegrate. 
The  freezing  of  sandstone  when  fresh  quarried  or  saturated 
with  water  is  therefore  very  injurious. 


16 


BUILDING  STONE  AND  BRICK 


§31 


When  water  freezes  in  the  crevices  or  spaces  between  the 
laminations,  its  action  is  that  of  a  wedge  tending  to  split  the 
rock  and  to  widen  the  crevice  more  and  more  with  each 
repetition  of  the  freezing  process.  By  this  means,  stones  of 
laminated  or  stratified  structure,  when  laid  on  edge,  are 
particularly  liable  to  disfigurement  by  exfoliation,  or  the 
scaling  of  the  surface.  In  the  large  cities,  it  is  not  uncom¬ 
mon  to  see  balusters  and  carved  details  partly  destroyed 
from  this  cause.  The  damage  from  the  freezing  of  water  in 
the  spaces  and  crevices  between  the  laminations  is  not  so 
great  when  the  stone  is  laid  on  its  bed  as  when  it  is  laid  on 
edge,  because  there  is  not  the  same  opportunity  for  the  space 
lying  in  a  horizontal  plane  to  collect  the  moisture  and  also 
because  the  pressure  on  the  stone  from  the  superimposed 
masonry  nullifies  to  some  extent  the  wedging  or  bursting 
action  of  the  freezing  water. 

The  severest  atmosphere  on  building  stone  is  one  that 
frequently  and  for  long  periods  contains  great  quantities  of 
suspended  moisture  in  the  shape  of  fogs  and  is  also  sub¬ 
jected,  by  environment,  to  much  smoke  and  gas  from  the 
bituminous  coals  of  manufactories.  Such  atmospheres  are 
likely  to  contain  carbonic-acid  gas  and  sulphurous  fumes, 
which  have  a  deleterious  effect  on  limestones  and  marbles. 
The  actions  from  these  sources  are  especially  marked  where 
the  atmosphere  is  extremely  moist. 

It  is  the  opinion  of  some  authorities  that,  as  a  cause  of 
decay,  the  carbonic  acid  is  of  little  importance  compared 
with  sulphurous  acid.  One  of  the  combustion  products  of 
coal  is  sulphur  dioxide,  S03.  This  gas  is  very  soluble  in 
water,  and  when  transferred  to  a  building  from  the  chimney, 
whence  it  issues,  it  will  combine  with  the  moisture  found  on 
the  stone  faces  and  form  sulphurous  acid,  H3S03.  If  car¬ 
bonate  of  lime  is  one  of  the  constituents  of  the  stone,  it  will 
be  decomposed  by  the  acid  and  cause  disintegration  of  the 
stone.  The  Parliament  House,  in  London,  may  be  cited  as 
an  example.  The  stones  of  this  building,  made  of  dolomite, 
were  selected  and  tested  for  durability  by  the  best  scientific 
and  technical  skill  in  Great  Britain,  but  the  corroding 


§31 


BUILDING  STONE  AND  BRICK 


17 


influence  of  the  London  atmosphere  has  been  such  that  it  is 
now  a  question  whether  the  building  will  last  as  long  as  if  it 
were  built  of  timber. 

Table  I,  taken  from  a  United  States  census  report,  gives 
the  length  of  time  that  the  several  varieties  of  stone  named 
have  lasted  in  New  .York  City  without  material  deterioration. 

TABLE  I 

DURABILITY  OF  BUILDING  STONE 


Variety  of  Stone 


Years 


Brownstone,  coarse . 

Brownstone,  fine  laminated  .  . 

Brownstone,  compact . 

Bluestone  (blue  shale)  .  .  .  . 
Sandstone,  Nova  Scotia  .  .  . 
Limestone,  Ohio,  best  silicious 
Limestone,  coarse  fossiliferous 

Limestone,  oolitic . 

Marble,  coarse  dolomite  .  .  . 

Marble,  fine  dolomite . 

Granite . 

Gneiss . 


5  to  15 

20  tO  50 
100  tO  200 
100  tO  200 

50  to  100 

100  tO  200 
20  tO  40 

30  to  40 
40  to  50 
50  to  100 
75  to  200 
50  to  200 


29.  Effect  of  Quarrying  and  Finishing. — Before 
stones  are  used  in  an  important  structure  they  must  be 
thoroughly  seasoned.  When  detached  from  the  rock,  stone 
is  generally  saturated  with  quarry  water.  It  should  there¬ 
fore  be  exposed  for  some  months,  preferably  under  cover,  to 
allow  this  water  to  evaporate.  If  the  stone  is  not  seasoned 
before  it  is  placed  in  the  wall  of  the  structure,  it  is  likely  to 
remain  damp,  and  the  excess  of  moisture,  in  freezing,  will 
influence  the  durability  of  the  material. 

The  use  of  heavy  explosives  for  detaching  dimension 
stone  is  detrimental  to  the  quality  of  durability,  owing  to  the 
fact  that  the  severe  concussion  is  likely  to  jar  the  particles 
and  partly  destroy  their  cementation  and  cohesion,  producing 


18 


BUILDING  STONE  AND  BRICK 


§31 

incipient  cracks  and  flaws  that  ,make  the  face  of  the  stone 
more  permeable  to  moisture  and  thus  hasten  the  destruction 
of  the  stone  by  freezing  and  chemical  action.  For  the  same 
reasons,  stones  sawed  to  size  are  more  durable  than  those 
hammered  and  broken;  and  stones  taken  from  the  quarry 
by  channeling  or  cutting  are  preferable  to  those  procured 
by  wedging. 

30.  Effect  of  Fire. — The  destructive  fires  that  occur 
in  the  large  cities  frequently  subject  the  stone  walls  of 
structures  to  intense  heat.  While  stone  is  an  excellent  non¬ 
conductor,  it  is  not  as  a  rule  so  durable,  when  subjected  to 
intense  heat,  as  brick. 

The  severest  test  to  which  a  stone  can  be  subjected  in  a 
fire  is  for  it  to  be  heated  intensely  and  then  cooled  by 
a  sudden  stream  of  water  from  a  fire-hose.  This  rapid 
change  of  temperature  causes  the  exterior  heated  layer  of 
the  stone  to  contract  more  rapidly  than  the  mass,  and  from 
many  stones  thus  treated,  large  pieces  will  crack  and  break 
off;  the  process,  if  repeated  several  times,  results  in  the  entire 
destruction  of  the  stone. 

The  silicious  sandstones  are  the  least  destructible  by  fire, 
while  the  granites  and  conglomerates  are  probably  the  most 
affected  by  intense  heat  and  the  sudden  cooling  incident  to 
the  application  of  water.  Limestones  are  very  refractory, 
that  is,  unaffected  by  heat,  in  temperatures  less  than  1,000°  F. 
and  at  this  temperature  are  not  liable  to  deterioration  by 
sudden  cooling,  though  above  this  temperature,  they  may  be 
reduced  to  quicklime,  which  crumbles  and  falls  away  after  a 
few  weeks’  exposure  to  the  air. 


STRENGTH  OF  STONES  AND  MASONRY 

31.  The  resistance  of  stones  to  stress  varies  greatly,  and 
the  strength  of  masonry  depends  not  only  on  the  materials 
of  which  it  is  composed  but  on  the  manner  in  which  these 
materials  are  handled;  that  is,  on  the  workmanship.  Stones 
that  are  the  densest  usually  possess  the  greatest  resistance, 


§31 


BUILDING  STONE  AND  BRICK 


19 


and  masonry  composed  of  squared  stones  with  close  joints 
is  the  strongest. 

Many  tables,  based  on  the  results  of  tests,  give  the  strength 
values  of  building  stones,  but  they  differ  widely,  the  dis¬ 
crepancy  being  due  to  the  following  causes: 

1.  Samples  are  taken  from  different  quarries  or  from 
different  parts  of  the  same  quarry. 

2.  The  pieces  of  stone  used  for  testing  are  not  uniformly 
seasoned. 

3.  Test  pieces  are  of  different  sizes. 

4.  They  are  not  uniformly  dressed  or  finished. 

5.  Variations  exist  in  the  method  of  placing  the  test 
specimens  in  the  testing  machine. 

Frequently,  stones  quarried  from  different  parts  of  the 
same  bed  will  vary  from  20  to  30  per  cent,  in  their  resistance 
to  crushing,  and  stones  that  have  been  quarried  for  some 
time  and  exposed  will  show  a  different  resistance  from  those 
lately  detached.  The  larger  the  test  piece,  the  greater  will 
be  the  unit  stress  developed,  because  small  cubes  do  not 
develop  so  great  a  unit  resistance  as  large  ones,  and  within 
certain  limits  the  unit  stress  that  test  cubes  of  the  same 
material  will  sustain  varies  directly  as  the  cube  of  the  sides. 

The  method  of  finishing  the  test  pieces  and  the  accuracy 
and  fineness  with  which  the  sides  are  dressed  have  much  to 
do  with  the  results  of  the  test.  Specimens  that  have  been 
sawed  to  shape  test  higher  than  those  that  have  been  finished 
with  a  tool  or  a  chisel.  A  microscopic  examination  of  the 
surface  finished  with  a  chisel  reveals  numerous  minute  cracks, 
caused  by  the  excessive  jars,  that  tend  to  reduce  the  crushing 
strength  by  starting  fractures.  The  fineness  of  the  surface 
finish  also  affects  the  result,  owing  to  the  fact  that  when  the 
bearing  surfaces  are  rough,  transverse  stresses  that  tend  to 
disrupt  the  specimen  are  created. 

32.  It  is  well  determined  that  from  lack  of  uniformity  of 
texture,  building  stones  and  masonry  of  the  same  material 
have  variable  strength  values.  This  uncertainty  regarding 
the  exact  strength  of  masonry  materials,  together  with  their 


/ 


TABLE  II 

STRENGTH  OF  BUILDING  STONES  AND  MASONRY 


Material 


Granite: 

Colorado . 

Connecticut . 

Massachusetts . 

Maine . 

Minnesota . 

New  York . 

New  Hampshire . 

Sandstone : 

Bluestone . 

Connecticut,  Middletown  .  .  . 
Massachusetts,  Longmeadow, 

brown . 

Massachusetts,  Longmeadow, 

red  . 

New  York,  Hudson  River  .  . 
New  York,  Little  Falls,  brown 

Ohio . 

Pennsylvania,  Hummelstown, 
brown . 

Limestone: 

New  York,  Kingston . 

New  York,  Garrison  Station  .  . 
Indiana,  Bedford,  oolitic  .  .  . 

Michigan,  Marquette . 

Pennsylvania,  Conshohocken  . 

Marble: 

Pennsylvania,  Montgomery 

County . .  . 

Massachusetts,  Lee,  dolomite  . 
New  York,  Pleasantville,  dolo¬ 
mite  . 

Italian . 

Vermont . 

Slate  . 

Rubble ,  in  lime  mortar . 


Weight 

per  Cubic  Foot 

Pounds 

Compressive 

Strength 

Pounds 

per  Square  Inch 

Tensile  Strength 

Pounds 

per  Square  Inch 

1 

Modulus  of 

Rupture 

Pounds 

per  Square  Inch 

1 66 

15,000 

1 66 

14,000 

1,500 

165 

16,000 

165 

15,000 

166 

25,000 

166 

16,000 

600 

1,800 

166 

12,000 

160 

15,000 

1,400 

2,700 

148 

7,000 

590 

1,000 

142 

10,000 

450 

149 

12,000 

450 

12,000 

10,000 

139 

8,000 

100 

479 

12,000 

168 

12,000 

164 

18,000 

Average 

Average 

146 

8,000 

1,000 

1,500 

146 

8,000 

15,000 

11,000 

22,800 

Average 

Average 

22,000 

700 

1,200 

168 

12,000 

167 

10,000 

160-180 

10,000 

10,000 

5,000 

150 

500 

20 


31 


BUILDING  STONE  AND  BRICK 


21 


usually  rapid  deterioration,  necessitates  the  use  of  a  high 
factor  of  safety,  so  that  in  all  work  of  this  class,  minimum 
safety  factors  ranging  from  10  to  20  are  employed.  When, 
therefore,  the  average  strength  values  of  commercial  masonry 
materials  are  known  and  a  high  factor  of  safety  is  used,  the 
basis  on  which  the  design  is  made  is  assuredly  safe. 

TABLE  III 

ALLOWABLE  UNIT  STRESSES  FOR  MASONRY  MATER  I  AES 


Description  of  Material 

Safe 

Compressive 

Stress 

Pounds  per 
Square  Inch 

Safe 

Bending 

Stress 

Pounds  per 
Square  Inch 

Capsto?ie ,  templets ,  monoliths : 

Bluestone  . 

700 

300 

Granite .  . 

700 

180 

Limestone . 

500 

150 

Marble . 

400 

120 

Sandstone,  other  than  bluestone  . 

350 

100 

Slate  .  .  . 

700 

400 

Squa  red-stone  mason  ry : 

Bluestone  .' . 

350 

Granite . 

350 

Limestone . 

250 

Sandstone,  other  than  bluestone  . 

175 

Rubble: 

Laid  in  Portland-cement  mortar  . 

150 

20 

Laid  in  natural-cement  mortar 

120 

Laid  in  lime-and-cement  mortar  . 

100 

Laid  in  lime  mortar . 

80 

33.  The  average  strength  values  of  masonry  materials, 
which  are  sufficiently  conservative  for  good  engineering 
practice,  are  given  in  Tables  II  and  III. 

34.  The  values  given  in  Table  II  are  the  average 
ultimate,  or  breaking,  loads  for  the  different  materials. 


22 


BUILDING  STONE  AND  BRICK 


31 


They  are  the  results  of  tests  made  at  different  times  on 
specimens  prepared  for  the  purpose.  It  will  be  noticed  that 
the  strength  values  of  squared  masonry  are  not  given,  and 
though  conservative  practice  recommends  that  masonry  of 
squared  stone  may  be  considered  as  having  an  ultimate 
strength  equal  to  four-tenths  the  strength  of  the  stone,  this 
is  merely  an  assumption  that  has  not  been  substantiated  by 
tests.  The  scarcity  of  reliable  tests  on  masonry  piers  and 
walls  is  due  to  the  fact  that  in  order  to  obtain  accurate  results 
of  the  test,  specimens  must  be  of  full-size  dimensions,  and 
when  thus  built  their  strength  is  so  great  as  to  resist  the 
ultimate  power  of  the  testing  machine. 

35.  In  using  the  values  given  in  Table  II,  factors  of 
safety  of  not  less  than  10  for  compression,  15  for  tension, 
and  from  10  to  20  for  bending  stress  should  be  employed. 
The  usual  practice  in  structural  and  architectural  engineering 
is  to  use  allowable  unit  values  for  masonry  and  masonry 
materials  as  given  in  Table  III.  These  values  are  considered 
good  practice,  and,  in  most  materials,  correspond  with  values 
recommended  by  the  building  laws  of  several  cities.  The 
ultimate  unit  bending  stress  is  called  the  modulus  of  rupture. 
Its  use  will  be  explained  in  a  later  Section. 


SELECTION  OF  BUILDING  STONES 


METHODS  OF  SELECTION 

36.  In  the  building  of  important  masonry  structures,  it 
is  of  prime  importance  that  the  stone  employed  shall  be 
of  sufficient  strength  and  durability.  Probably  nothing  in 
engineering  construction  is  so  neglected  as  the  inspection  of 
the  building  stone  that  is  to  be  used. 

If  it  is  necessary  to  employ  great  quantities  of  building 
stone  at  points  where  the  stability  of  the  structure  depends 
on  the  strength  of  the  stone,  an  inspection  of  the  quarry 
from  which  the  stone  is  to  be  obtained  should  be  made. 


§31 


BUILDING  STONE  AND  BRICK 


23 


Besides,  it  should  be  the  effort  of  the  engineer  to  inspect 
some  building  or  structure  that  has  been  erected  of  the  same 
material  for  a  considerable  length  of  time. 

It  is  well,  however,  not  to  depend  wholly  on  either  inspec¬ 
tion  at  the  quarry  or  at  the  building,  but  to  subject  the  stone 
to  laboratory  tests,  when  it  should  be  tested  both  chemically 
and  physically,  as  well  as  subjected  to  microscopic  inspection. 

37.  Inspection  of  Stone  at  Quarry. — The  inspection 
at  the  quarry,  when  carefully  made,  will  frequently  reveal 
the  durability  as  well  as  the  uniformity  of  the  stone. 
Exposed  quarry  faces  will  sometimes  show  the  weathering 
properties  of  the  stone,  besides  its  liability  to  disintegration 
caused  by  moisture  and  running  water  containing  deleterious 
acids  and  alkalies.  Such  an  inspection  will  also  determine 
whether  there  is  sufficient  stone  of  a  uniform  texture  and 
color  in  sight  to  supply  the  amount  of  material  required  for 
the  work.  By  quarry  inspection  likewise,  the  several  grades 
of  stone  are  known,  and  in  first-class  work  it  is  imperative 
that  the  best  grade  of  the  quarry  be  insisted  on.  Frequently 
a  poor  grade  of  stone  is  employed  in  the  structure,  and  on 
showing  deterioration  and  poor  weathering  qualities  causes 
otherwise  excellent  building  stone,  when  of  first-class  cut¬ 
tings,  to  be  condemned. 

38.  Inspection  of  Stone  in  Buildings. — By  inspecting 
stone  that  has  been  in  place  in  a  building  or  structure  for  a 
considerable  length  of  time,  an  excellent  idea  may  be  had  of 
its  durability  as  to  structure,  color,  and  weathering  properties. 
If,  after  years  of  exposure  in  the  atmosphere  of  an  industrial 
city  situated  in  the  temperate  zone,  the  building  stone  shows 
no  disintegration  and  has  retained  its  original  luster  and 
color,  except  for  the  soil  of  dust  and  smoke  stains,  it 
certainly  can  be  considered  of  the  best  structural  value  for 
building  purposes. 

39.  Laboratory  Tests  of  Stone. — While  the  quarry 
and  building  inspections  of  stone  are  of  the  utmost  practical 
importance,  they  should,  as  previously  stated,  be  augmented 
by  laboratory  tests.  When  the  stone  to  be  used  is  from  a 

211—8 


24 


BUILDING  STONE  AND  BRICK 


§31 


new  quarry,  the  characteristics  of  the  product  are  little 
known.  The  laboratory  tests  usually  consist  of  chemical 
analysis ,  microscopic  examinations ,  and  physical  tests. 

40.  The  chemical  analysis  determines  both  qualita¬ 
tively  and  quantitatively  the  chemical  constituents  of  the 
stone.  Examined  qualitatively,  the  mineral  elements  and 
chemical  combinations  comprising  the  stone,  together  with 
the  impurities  and  organic  matter,  are  determined;  while  the 
quantitative  analysis  shows  the  proportions  of  the  different 
elements  and  chemical  combinations.  When  the  chemical 
composition  of  a  stone  is  in  this  way  determined,  conclusions 
can  usually,  though  not  always,  be  drawn  as  to  the  durability 
and  the  weathering  properties  of  the  stone. 

41.  The  microscopic  examination  of  building  stone 
is  of  more  importance  and  is  less  expensive  to  conduct  than 
the  chemical  analysis,  for  by  it  is  revealed  the  structure  of 
the  stone.  By  the  microscope  may  be  observed  the  size  and 
shape  of  the  particles  or  crystals  composing  the  stone,  their 
relative  closeness,  and  the  character  and  compactness  of  the 
cementing  material  holding  them  together.  Usually,  the 
mineral  constituents  of  the  stone  may  be  determined  like¬ 
wise  by  microscopic  examination  and  frequently  their  pro¬ 
portions  may  be  estimated,  together  with  the  percentage  of 
impurities  contained  in  the  stone.  Likewise,  by  the  micro¬ 
scope  may  be  detected  any  flaws  in  the  structure,  such  as 
cracks,  cavities,  incipient  fractures,  and  gas  bubbles. 

42.  The  physical  tests  of  a  stone  furnish  data  from 
which  a  fair  estimate  of  the  durability  may  be  made.  It 
includes  the  determination  of  the  resistance  to  crushing  and 
transverse  stresses,  and  the  resistance  to  abrasion,  heat,  and 
cold.  In  making  these  tests,  the  object  is  to  impose  on  the 
stone  as  nearly  as  possible  conditions  that  in  the  course  of 
a  few  hours  or  a  few  weeks  will  approximate  the  effect 
produced  by  actual  use  during  a  lapse  of  years. 


BUILDING  STONE  AND  BRICK 


25 


§31 


METHODS  OF  TESTING  STONE 

43.  Absorptive  Power. — Few  of  the  properties  of  a 
stone  are  of  greater  importance  than  the  absorptive  power, 
since  it  is  largely  through  the  freezing  of  the  absorbed 
water  that  the  majority  of  stones  are  destroyed.  The 
absorptive  power  of  a  stone  is  usually  ascertained  by  two 
tests — one  to  determine  the  absorption  from  a  moist  atmos¬ 
phere,  and  one  to  determine  the  amount  of  water  absorbed 
through  actual  soaking. 

The  first  test  is  performed  by  keeping  samples  of  the 
stone  in  hot,  dry  air  for  several  days  to  expel  the  hydro¬ 
scopic  moisture,  after 
which  they  are  weighed. 

They  are  then  placed  on 
shelves  in  a  cylinder,  the 
mouth  of  which  is  sealed 
with  water  by  placing 
the  cylinder,  mouth 
down,  in  a  pan  of  water. 

The  cylinder  and  the 
samples  are  kept  for 
several  weeks  in  a 
temperature  ranging 
between  60°  and  70°  F., 
the  water, being  replenished  from  time  to  time  so  as  to 
maintain  a  constant  seal  at  the  mouth  of  the  cylinder.  At 
the  end  of  the  test  period,  the  samples  are  weighed.  The 
increase  in  weight  shows  the  amount  of  absorption  that  will 
take  place  in  moist  air. 

To  ascertain  the  amount  of  water  absorbed  by  soaking, 
the  specimens  of  stone  are  dried  and  weighed,  then  immersed 
in  water  for  24  hours,  removed,  and  weighed  again;  the 
increase  in  weight  will  be  the  amount  of  absorption.  This 
is  usually  expressed  in  a  percentage  of  the  weight  of  the 
dry  stone.  An  absorption  of  more  than  3  per  cent,  is 
regarded  as  detrimental. 

The  average  water  absorbed  by  stones  is  shown  in  Table  IV. 


TABLE  IV 

ABSORPTIVE  POWER  OF  STONES 


Stone 

Absorptive  Capacity 
Per  Cent. 

Granites  .  .  . 

.066  to  .155 

Sandstones  .  . 

.410  to  5.480 

Limestones  .  . 

.200  to  5.000 

Marbles  .  .  . 

.080  to  .160 

Trap . 

.000  to  .019 

26 


BUILDING  STONE  AND  BRICK 


.31 


44.  The  amount  o.f  water  absorbed  depends  largely  on 
the  density  of  the  stone;  a  dense  stone  absorbs  less  than  a 
porous  stone.  Stones  that  have  already  begun  to  decom¬ 
pose  absorb  a  much  larger  quantity  of  water  than  those 
fresh  from  the  quarry.  A  low  absorption  is  generally  con¬ 
sidered  as  indicating  a  good  quality;  still  it  does  not  follow 
that  a  stone  that  absorbs  a  small  amount  of  water  will  suffer 
the  least  through  the  action  of  frost,  for  the  reason  that  a 
porous  stone  of  coarse  structure  will  dry  more  rapidly  than 
one  of  a  firmer  grain  and  open  texture,  and  will  permit  the 
expansive  action  of  freezing  water  to  find  relief  without 
forcing  apart  the  particles  of  which  the  stone  is  composed. 
Hence,  a  high  rate  of  absorption  is  more  detrimental  to  a 
fine-grained  stone  than  to  a  coarse-grained  one. 

45.  Resistance  to  Freezing. — To  ascertain  the  ability 
of  a  stone  to  resist  the  expansive  action  of  freezing  water, 
several  tests  are  recommended.  Brard’s  test,  which  con¬ 
sists  in  boiling  weighed  samples  in  a  concentrated  solution 
of  sulphate  of  soda,  is  considered  the  best.  The  soda  in 
crystallizing  expands,  as  does  water  when  freezing.  After 
each  boiling,  the  stone  is  removed  from  the  solution  and 
hung  up  to  dry.  The  operation  is  repeated  daily  during  a 
period  of  4  weeks,  after  which  the  stone  is  dried  and  weighed 
and  the  difference  in  weight  and  the  general  appearance  are 
noted. 

46.  Resistance  to  Abrasion. — The  resistance  of  a 
stone  to  abrasion  is  ascertained  by  placing  cleaned  and 
weighed  fragments  of  the  stone  in  a  metal  cylinder  and 
revolving  it  at  the  rate  of  about  30  turns  a  minute  until 
10,000  revolutions  have  been  made.  As  the  cylinder 
revolves,  the  stones  are  rolled  against  one  another,  and  the 
edges  are  gradually  broken  off,  the  particles  thus  separated 
forming  a  dust.  When  the  required  number  of  revolutions 
has  been  reached,  the  stone  is  removed  from  the  cylinder 
and  weighed.  The  difference  between  the  two  weighings 
represents  the  loss  by  abrasion.  The  ability  of  stones  to 
resist  abrasion  is  compared  by  the  ratio  of  the  weight  of  the 


§31 


BUILDING  STONE  AND  BRICK 


27 


dust  worn  off  to  the  original  weight  of  the  stone,  and  the 
loss  is  expressed  as  per  cent,  of  wear.  Thus,  if  the  original 
weight  of  the  stone  placed  in  the  cylinder  was  20  pounds, 
and  the  weight  of  the  dust  produced  was  5  pounds,  the  loss 
would  be  expressed  as  25  per  cent,  of  wear. 

Regarding  the  ability  of  stones  to  resist  abrasion,  it  may 
be  stated  generally  that  the  granite  rocks  lose  from  2  to 
10  per  cent.;  the  range  of  loss  in  limestone  rocks  varies 
from  10  to  35  per  cent.;  and  sandstones  lose  about  14  per  cent. 

The  resistance  to  abrasion  by  wind-blown  sand  is  ascer¬ 
tained  by  subjecting  weighed  samples  of  the  stone  to  the 
action  of  a  sand  blast  operated  under  a  given  pressure  for  a 
specified  time,  at  the  end  of  which  the  sample  is  weighed  to 
ascertain  the  loss. 

47.  Crushing  Strength. — The  crushing  strength 
of  a  stone  is  ascertained  by  subjecting  cubical  specimens 
accurately  dressed  to  form  and  dimensions  to  a  measured 
force  applied  in  a  suitably  constructed  machine,  until  they 
are  crushed. 

48.  Bending  Strength. — To  ascertain  the  bending 
strength  of  a  stone,  prisms  1  inch  square  and  from  6  to 
12  inches  long  are  supported  at  each  end  and  loaded  in  the 
center  until  fracture  takes  place.  The  breaking  load  thus 
found  is  employed  to  ascertain  the  breaking  load  of  any 
stone  under  transverse  stresses.  Owing  to  the  uncertainty 
regarding  the  strength  of  stone,  a  working  strength  of  from 
10  to  20  per  cent,  of  the  ultimate  strength  is  used. 

49.  Permanence  of  Color. — In  order  to  ascertain  the 
permanence  of  color  of  a  stone,  samples  are  placed  in  an 
air-tight  vessel  and  submitted  to  the  action  of  the  fumes  of 
nitric,  hydrochloric,  and  other  acids  for  a  period  of  7  or  more 
weeks.  At  the  end  of  this  time  the  stones  are  washed  and 
any  change  in  color  is  noted. 

50.  Resistance  to  Acids. — The  effect  of  the  acids 
contained  in  the  atmosphere  is  determined  by  immersing 
samples  of  the  stone  for  several  days  in  water  that  contains 


28 


BUILDING  STONE  AND  BRICK 


§31 


1  per  cent,  of  the  acid  whose  action  it  is  desired  to  ascertain, 
and  agitating  frequently.  The  usual  acids  contained  in  the 
air  are  sulphuric  and  nitric  acid,  due  to  the  smoke  in  large 
cities. 

i 

51.  Specific  Gravity. — The  determination  of  the  spe¬ 
cific  gravity  of  stone  affords  a  convenient  method  of  ascer¬ 
taining  the  weight  per  cubic  foot.  This  determination  is 
made  by  carefully  weighing  a  small  piece  of  the  stone  in  the 
air  and  then  weighing  it  in  water.  The  result  obtained  by 


TABLE  V 

SPECIFIC  GRAVITY  AND  WEIGHT  OF  STONE 


Kind  of  Stone 

Specific  Gravity 

Weight 

Pounds  per  Cubic  Foot 

Minimum 

Maximum 

Minimum 

Maximum 

Granite  .  .  . 

2.6o 

2.80 

163 

170 

Sandstone  .  . 

2.23 

2-75 

137 

170 

Limestone  .  . 

1 .90 

2-75 

1 18 

175 

Marble  .  .  . 

2.62 

2-95 

165 

179 

dividing  the  weight  in  air  by  the  difference  between  the 
weight  in  air  and  the  weight  in  water  is  the  specific  gravity, 
which  multiplied  by  62.5,  the  weight,  in  pounds,  of  1  cubic 
foot  of  water,  gives  the  weight  of  1  cubic  foot  of  the  stone. 

When  it  is  desired  to  ascertain  the  specific  gravity  of  porous 
stones,  or  those  which  absorb  considerable  water,  the  speci¬ 
men  is  first  weighed  dry,  then  immersed  in  water,  and, 
when  thoroughly  saturated,  removed  and  weighed,  again 
immersed,  and  weighed  while  under  water.  The  quotient 
obtained  by  dividing  the  dry  weight  by  the  difference 
between  the  weights  of  the  saturated  stone  in  air  and  under 
water  will  be  the  specific  gravity. 

Table  V  contains  the  specific  gravity  and  weight  per  cubic 
foot  of  the  usual  building,  stones. 


§31 


BUILDING  STONE  AND  BRICK 


29 


52.  Resistance  to  Fire. — The  power  of  a  stone  to 
resist  the  action  of  high  temperatures  is  ascertained  by 
heating  samples  to  a  red  heat  in  a  muffle  furnace  and 
observing  the  effect.  When  slightly  cooled,  the  heated 
samples  are  plunged  into  cold  water  and  the  effect  in  pro¬ 
ducing  cracks  or  crumbling  is  noted.  ' 


BRICK 


INTRODUCTION 

53.  Brick  may  be  called  artificial  stone  manufactured  in 
small  pieces  for  convenience  in  laying.  Among  bricks  are 
included  ordinary  clay  brick ,  firebrick ,  terra  cotta ,  and  sand- 
lime  brick.  While  there  are  many  artificial  stones  manu¬ 
factured,  they  will  not  be  discussed  in  this  Section.  Terra 
cotta  is  much  used  in  modern  construction  to  obtain  decora¬ 
tive  and  architectural  effect,  but  its  chief  structural  use  is  in 
the  construction  of  fireproof  floors,  partitions,  and  coverings. 

The  material  used  in  the  manufacture  of  common  brick  is 
clay  that  has  a  variable  percentage  of  protoxide  of  iron. 
Other  substances  that  form  part  of  ordinary  clay  either  do 
no  good  or  are  absolutely  harmful,  carbonate  of  lime  in  any 
large  quantity,  for  instance,  rendering  the  clay  unfit  for 
brickmaking.  Sand  or  silica  should  not  exist  in  any  excess¬ 
ive  quantity,  as  an  excess  of  sand  renders  the  brick  too 
brittle  and  destroys  cohesion. 

The  protoxide  of  iron  in  the  brick  clay  causes  the  red 
color  in  the  brick  after  burning,  the  color  varying  with  the 
proportion  of  iron.  With  more  intense  heat,  the  brick,  if 
slightly  fusible,  may  be  vitrified  externally  and  thus  become 
a  sort  of  greenish  blue.  The  presence  of  magnesia  or  a 
small  percentage  of  lime  in  the  clay  will  change  the  red 
color  produced  by  iron  to  a  cream  or  buff  shade.  In  the 
mottled  brick  now  largely  used,  the  mottled  effect  is  pro¬ 
duced  by  using  coloring  matter  in  the  clay  or  by  mixing 
clays  of  different  chemical  composition. 


30 


BUILDING  STONE  AND  BRICK 


§31 


CLAY  BRICK 


IIAND-MADE  BRICK 

54.  In  many  localities  where  brick  are  to  be  manufac¬ 
tured  for  only  a  short  period,  or  in  country  districts  where, 
even  if  the  plant  were  permanent,  it  would  often  be  idle  on 
account  of  no  building  being  done,  it  is  sometimes  more 
economical  to  make  brick  by  hand  than  to  put  in  brick¬ 
manufacturing  machinery. 

When  making  brick  by  hand,  the  clay,  after  water  is  added, 
is  worked  in  a  circular  pit,  usually  about  2  feet  6  inches  deep 
and  15  feet  in  diameter.  In  the  center  of  this  pit  is  a  brick 
or  stone  pier  with  a  vertical  pin  fastened  in  its  center. 
Pivoted  to  this  pin  is  a  horizontal  shaft  with  a  wheel,  and 
this  wheel  rests  on  the  clay  that  has  been  thrown  into  the 
pit.  If  a  horse,  hitched  to  the  outer  end  of  the  shaft,  is 
made  to  walk  around  the  pit,  the  shaft  will  swing  around  the 
vertical  pin,  while  the  wheel  will  revolve  and  churn  the 
mixture  of  clay  and  water.  When  the  clay  becomes  soft, 
it  is  taken  to  the  molding  table  and  pressed  into  molds 
by  hand. 

The  molds,  which  have  neither  top  nor  bottom,  are  usually 
made  of  wrought  iron  and  wood  or  cast  iron  or  brass.  When 
it  is  desired  to  make  an  indentation,  called  a  frog ,  or  kick , 
in  one  side  of  the  brick,  so  as  to  give  a  better  bond  to  the 
mortar,  the  mold  is  set  on  a  stock  board ,  or  bottom ,  made  to 
fit  it  and  having  a  projection  the  shape  of  the  desired  frog. 
The  top  of  the  mold  is  always  struck  flush  with  a  steel  or  a 
wooden  straightedge.  When  laying  brick  containing  a  frog 
in  one  side,  the  frog  side  is  placed  upwards.  In  wire-cut 
machine  brick,  of  course,  there  can  be  no  frogs,  but  frogs 
are  often  made  even  in  both  sides  of  pressed  brick. 

Before  filling  the  brick  molds,  they  are  either  dipped  in 
water  (called  slop  molding )  or  in  sand  (called  dry  molding ) 
to  prevent  the  clay  from  adhering  to  the  mold.  Sand  mold¬ 
ing  gives  cleaner  and  sharper  brick  than  slop  molding. 


I 


3 31  BUILDING  STONE  AND  BRICK  31 

After  the  brick  are  shaped  in  the  mold,  they  are  laid  in  the 

l 

sun  or  in  a  dry  house  for  3  or  4  days,  after  which  they  are 
stacked  in  kilns  and  fired. 


MAC  HIKE-MADE  BRICK 

55.  Where  many  brick  are  to  be  made,  the  work  is 
usually  done  by  machinery,  and  one  of  three  methods,  known 
as  the  soft-mud ,  the  stiff-mud ,  and  the  dry-clay  process ,  is 
employed. 

56.  Soft-Mud  Process. — In  the  soft-mud  process, 
the  clay  is  thrown  into  a  plank-lined  pit,  whefe  it  is  soaked  in 
water  for  24  hours.  The  usual  custom  is  to  provide  several 
pits,  so  that  one  pit  may  always  contain  clay  that  has  been 
softened  by  the  water  and  is  ready  for  use  while  the  other 
pits  are  being  filled  or  the  clay  is  in  the  process  of  softening. 
In  some  localities  where  the  clay  is  somewhat  wet  in  the  clay 
bank,  or  where  a  lower  grade  of  brick  is  being  made,  the  clay 
is  not  made  wet  until  it  is  placed  in  the  machine. 

From  the  softening  pit,  the  clay  is  taken  by  a  conveyer 
and  dropped  into  a  hopper,  from  the  bottom  of  which  it 
passes  into  one  end  of  a  trough.  Down  the  axis  of  this 
trough  runs  a  revolving  shaft,  along  the  length  of  which' are 
knife  blades  set  on  an  angle,  like  the  blades  of  a  ship  pro¬ 
peller.  This  shaft  with  its  blades  is  known  in  the  machine 
trade  as  a  screw  conveyer ,  or  worm.  This  worm  works  the 
clay  to  the  end  of  the  trough  farthest  from  the  hopper.  If 
the  clay  has  not  been  soaked  in  the  softening  pits,  it  is  wetted 
in  the  trough  by  means  of  a  spray,  which  spreads  the  water 
evenly  and  thus  prevents  unequal  wetting.  The  blades  of 
the  worm  help  to  mix  the  clay  completely  and  make  it  homo¬ 
geneous.  At  the  end  of  the  trough  is  a  plunger  that  works 
up  and  down  and  forces  the  clay  into  a  wooden  mold  that  is 
divided  into  six  compartments,  each  one  being  the  size  of  a 
brick.  The  mold  is  taken  out  of  the  machine  at  each  stroke 
of  the  plunger  and  a  new  one  inserted,  the  brick  being  emptied 
out  of  the  mold  on  a  board  and  then  taken  to  the  drying  yard, 

i 

where  they  are  allowed  to  dry  before  being  burned. 


32 


BUILDING  STONE  AND  BRICK 


31 


57.  Stiff-Mud  Process. — In  the  stiff-mud  process, 
the  clay  is  first  thoroughly  ground,  and  just  enough  water  is 
added  to  make  a  stiff  mud.  After  this  mud  is  mixed  and 
tempered  in  a  pug  mill ,  it  is  placed  in  a  machine  having  a 
die  the  exact  size  of  the  brick  required.  The  opening  in  this 
die  is  made  the  size  of  either  the  end  or  the  side  of  a  brick. 
The  machine  forces  a  continuous  bar  of  clay  through  this 
die,  and  as  it  emerges  it  is  automatically  cut  into  bricks, 
which  are  then  taken  to  the  drying  yard.  The  soft  brick  are 
placed  in  rows  in  a  yard  covered  by  a  rough  shed  with  open 
sides,  where  they  are  sun  or  air  dried  for  3  or  4  days.  When 
properly  dried  and  before  burning,  they  resemble  somewhat 
the  “adobe”  brick  that  were  formerly  used  for  constructing 
houses  and  are  still  employed  in  the  southwestern  part  of  the 
United  States,  and  also  in  Mexico  and  Central  America. 

58.  Dry-Clay  Process. — The  process  often  employed 
in  the  best  work  is  the  dry-clay  process.  In  this  method 
of  manufacturing  brick,  the  clay  is  used  just  as  it  comes  from 
the  bank,  and  is  apparently  perfectly  dry.  It  contains,  how¬ 
ever,  about  from  7  to  10  per  cent,  of  moisture.  The  clay  is 
dug  from  its  bed  and  stored  in  mounds,  sometimes  called 
kerfs ,  to  allow  the  mass  to  disintegrate.  It  is  usually  kept 
in  this  manner  for  two  or  three  winters,  as  frost  seems  to 
have  a  good  effect  on  it,  and  brick  made  from  clay  thus 
weathered  will  not  warp  in  the  kiln.  In  England,  the  clay 
used  for  making  the  very  best  brick  is  frequently  stored  in 
cellars.  After  the  clay  has  been  stored  for  a  sufficient  length 
of  time — although  often,  due  to  rush  of  business,  it  is  not 
kept  at  all — it  is  forced  through  a  perforated  plate,  called  a 
dry  pan ,  and  is  then  screened.  In  some  localities,  it  is  neces¬ 
sary  in  making  brick  to  mix  several  kinds  of  clay  to  get  the 
best  results.  After  screening,  the  clay  is  filled  loosely  into 
molds.  These  molds  are  of  the  same  width  and  length  as 
the  brick,  but  are  deeper  than  the  required  thickness  of  the 
brick.  A  plunger  is  then  forced  in  the  mold  under  heavy 
pressure  and  compresses  the  clay  to  the  size  of  the  brick 
desired.  The  brick  are  then  removed  to  the  kiln  and  fired. 


§31 


BUILDING  STONE  AND  BRICK 


33 


Molded  brick  are  made  in  the  same  way,  the  difference 
being  that  the  box  is  made  to  give  the  special  shape  of  the 
brick  required. 

Whenever  the  term  pressed  brick  is  used,  it  should  mean 
the  brick  made  by  the  dry-clay  process.  There  are  many 
so-called  dressed ,  or  face ,  brick ,  however,  that  are  made  by 
recompressing  soft-mud  brick. 


BRICK  BURNING 

59.  The  brick,  after  drying,  are  built  in  a  large  mass,  or 
kiln,  containing  from  100,000  to  300,000  brick.  Eyes,  or  flues, 
are  left  at  the  bottom  as  receptacles  for  fuel.  The  brick  are 
laid  loosely  together  in  order  to  allow  the  heat  to  pass  in  and 
around  them.  When  ready,  a  fire  is  started,  slowly  at  first, 
but  afterwards  increased  to  an  intense  heat;  and  after  burn¬ 
ing  for  a  period  determined  partly  by  the  fuel  used,  but 
mainly  by  experience,  the  fires  are  allowed  to  die  out  gradually. 

On  opening  a  brick  kiln  after  burning,  the  quality  of  the 
brick  therein  contained  may  be  divided  into  four  classes: 
(1)  The  extreme  outside,  or  first,  layer  contains  brick  that 
are  burnt  so  little  that  they  are  almost  worthless.  (2)  In 
the  second  layer  the  brick  are  underburned  and  soft;  these 
are  called  pale ,  or  salmon ,  brick ,  and  are  unfit  for  foundation 
or  face  work;  but  are  used  for  filling  in  between  stud  parti¬ 
tions,  and  sometimes  between  harder  brick  in  the  inside 
of  walls,  although  their  use  for  this  purpose  is  not  recom¬ 
mended.  (3)  In  the  third  layer  of  the  mass  forming  the 
kiln  is  found  a  class  of  brick  well  burned,  hard,  well  shaped, 
and  of  a  good  red  color;  this  kind  of  brick  is  good  for  any 
purpose.  (4)  The  brick  in  the  fourth,  or  inner,  layer  of  the 
kiln,  just  above  the  flues,  are  overburnt,  very  hard,  very 
brittle,  and  usually  distorted,  cracked,  and  even  vitrified; 
they  should  not  be  used  in  any  structure  subject  to  shock, 
but  are  often  employed  for  paving. 


34 


BUILDING  STONE  AND  BRICK 


31 


CLASSIFICATION  OF  CLAY  BRICK 

60.  Common  Brick. — The  term  common  brick 
includes  all  brick  that  are  intended  for  structural  and  not  for 
ornamental  purposes,  and  that  require  no  special  pains  to  be 
taken  in  their  manufacture.  There  are  three  grades  of  com¬ 
mon  brick,  termed,  according  to  their  position  in  the  kiln: 
arch,  or  clinker ,  brick;  red ,  hard ,  or  well-burned ,  brick;  and 
soft,  or  salmon,  brick. 

61.  Pressed,  or  Face,  Brick. — The  brick  called 
pressed,  or  face,  brick  are  hard  and  smooth  and  have 
sharp  corners.  They  are  usually  made  by  the  dry-clay 
process,  or  else  they  are  recompressed  brick.  Owing  to  the 
fact  that  these  brick  cost  more  than  common  brick,  they  are 
seldom  used  except  for  facing  walls  built  of  cheaper  grades 
of  brick. 

The  special  forms  of  pressed  brick  are  called  molded, 
gauged,  arch,  and  circle  brick.  Molded  and  ornamental  brick 
are  now  manufactured  in  a  great  variety  of  forms  and  pat¬ 
terns,  so  that  cornices  and  moldings  may  be  constructed 
entirely  of  brick.  If  an  architect  or  engineer  requires  special 
patterns  of  molded  brick  to  carry  out  designs,  most  of  the 
larger  companies  manufacturing  pressed  brick  will  make  the 
special  shapes  desired  if  drawings  are  furnished.  These 
should  be  drawn  to  a  large  scale,  and  full-sized  details  should 
be  given. 

62.  Stock  Brick. — Hand-made  brick  intended  for  face 
work  are  called  stock  brick,  and  in  manufacturing  and  burn¬ 
ing  them,  greater  care  is  taken  than  with  common  brick.  Stock 
brick  are  used  extensively  for  the  outside  facing  of  factories, 
machine  shops,  and  the  cheaper  class  of  private  dwellings. 
In  the  Eastern  States,  they  are  sometimes  called  face  brick. 

63.  Arcli  and  Circle  Bricks. — For  circular  or  seg¬ 
mental  doors  and  window  openings  in  brickwork,  arch 
brick  should  be  made  in  the  form  of  a  truncated  wedge,  that 
is,  a  wedge  with  the  sharp  end  cut  off.  The  walls  of  circular 
towers,  bay  windows,  etc.  are  faced  with  the  so-called  circle 


§31 


BUILDING  STONE  AND  BRICK 


35 


brick,  or  brick  molded  to  the  curvature  of  the  circle  desired. 
The  radius  of  the  bay  or  the  tower  should  always  be  given 
when  ordering  the  brick. 

64.  Firebrick. — The  brick  used  for  lining  furnaces, 
lime  kilns,  fireplaces,  and  tall  chimneys  in  factories  are  called 
firebrick.  They  should  be  free  from  cracks,  of  homoge¬ 
neous  composition  and  texture,  uniform  in  size,  of  a  regular 
shape,  easily  cut,  and  not  fusible.  They  are  usually  some¬ 
what  larger  than  the  ordinary  building  brick,  and  are  made 
of  a  very  pure  clay  and  clean  sand,  or  sometimes  of  pure 
silica  cemented  with  a  small  proportion  of  clay.  The  clay 
should  be  silicate  of  alumina.  Oxide  of  iron  in  the  clay  is 
very  injurious,  and  if  it  reaches  6  per  cent.,  the  brick  is  not 
suitable  for  the  purpose.  Specifications  for  firebrick  should 
require  that  the  oxide  of  iron  be  less  than  this  amount,  and 
that  the  aggregate  of  lime,  soda,  potash,  and  magnesia  be 
less  than  3  per  cent.  The  sulphide  of  iron,  or  pyrites,  has  a 
harmful  effect  on  the  fireclay,  and  brick  containing  it  should 
not  be  accepted.  An  excess  of  silica  in  the  brick  makes  it 
refractory  in  extremely  high  temperatures.  Where  the  brick 
has  to  resist  the  action  of  metallic  oxides,  which  would  have 
a  tendency  to  unite  with  silica,  alumina  should  be  in  excess. 

65.  Glazed  and  Enameled  Brick. — Brick  that  are 
either  glazed  or  enameled  are  used  largely  for  lining  water- 
closet  and  bathroom  walls,  the  wainscoting  of  halls  and 
staircases,  and  in  many  cases  the  entire  walls  of  stores, 
restaurants,  hospitals,  public  waiting  rooms,  and  markets, 
or  wherever  a  non-absorbent  surface  that  is  clean  and  light 
is  desired.  Glazed  and  enameled  brick  can  be  used  for  the 
exterior  of  buildings  as  well  as  for  the  interior,  as  they  will 
withstand  the  most  severe  changes  of  weather,  reflect  light, 
acquire  no  odor,  are  impervious  to  moisture,  and  are  fireproof. 

There  are  two  kinds  of  enameled  brick  known  to  the 
trade,  namely,  glazed  brick  and  enameled  brick.  Glazed 
brick  are  made  by  coating  the  unburned  brick  on  the  side  on 
which  it  is  to  be  glazed  with  a  slip ,  and  then  putting  on  a 
coat  of  transparent  glaze  closely  resembling  glass.  The 


36 


BUILDING  STONE  AND  BRICK 


§31 


slip,  which  gives  the  brick  its  white  color,  is  a  composition 
of  ball  clay,  pulverized  kaolin,  flint,  and  feldspar. 

In  a  genuine  enameled  brick,  the  enamel  is  fused  directly 
into  the  brick  without  any  intermediate  coat,  and  the  enamel 
in  itself  is  opaque. 

66.  An  enameled  surface  can  be  distinguished  from  one 
that  is  merely  glazed  by  chipping  off  a  piece  of  the  brick. 
The  enameled  brick  will  show  no  line  of  demarcation 
between  the  body  of  the  brick  and  the  enamel,  while  the 
glazed  brick  will  show  a  layer  of  slip  between  the  glaze  and 
the  brick.  Brick  are  enameled  or  glazed  only  on  one  face  or 
on  one  face  and  one  end. 

Genuine  enameled  brick  cost  more  than  glazed  brick,  as 
they  are  more  difficult  to  manufacture;  but,  owing  to  the 
enamel  being  a  part  of  the  brick  itself,  an  enameled  brick 
will  not  chip  or  peel  so  readily  as  a  glazed  brick,  and  is 
therefore  more  desirable. 

67.  The  genuine  enameled  brick  are  made  from  a  certain 
kind  of  clay  that  usually  contains  a  large  quantity  of  fireclay. 
The  enamel  is  applied  to  the  brick  either  before  or  after  it  is 
burned,  the  latter  method  producing  the  best  brick. 

For  many  years  all  the  glazed  and  enameled  brick  were 
made  in  England,  but  there  are  now  several  factories  in  the 
United  States.  Many  of  the  American  manufacturers  make 
the  American  standard  size,  which  is  8*  in.  X  4  in.  X  2i  in., 
but  some  of  them  adhere  to  the  English  standard  size,  which 
is  8f  in.  X  4i  in.  X  2i  in.  However,  the  sizes  of  brick  vary 
a  great  deal  in  different  sections  of  the  country. 

68.  Paving  Brick. — The  stiff-mud  process  is  generally 
employed  in  the  manufacture  of  paving  brick,  the  brick 
being  recompressed  to  give  them  better  shape.  They  are 
composed  of  about  three  parts  of  shale  clay  to  one  part  of 

fireclay,  and  are  burned  to  the  point  of  vitrification;  that  is, 

* 

to  a  heat  at  which  they  begin  to  fuse.  These  brick  have  a 
high  crushing  strength  and  absorb  very  little  moisture. 
They  are  used  principally  for  paving  driveways,  and  occa¬ 
sionally  for  paving  flat  roofs  on  fireproof  buildings. 


§31 


BUILDING  STONE  AND  BRICK 


37 


TERRA  COTTA 

69.  Varieties  and  Manufacture  of  Terra  Cotta. 

9 

There  are  three  varieties  of  terra  cotta,  the  porous ,  the  semi- 
porous,  and  the  de?ise.  The  degree  of  density  depends  on  the 
materials  used  in  its  manufacture. 

70.  The  porous  terra  cotta  is  produced  by  mixing 
a  plastic  clay  with  from  25  to  35  per  cent,  of  sawdust,  mold¬ 
ing  this  mixture  into  the  forms  desired,  and  then  subjecting 
it  to  intense  heat.  The  heat  will  transform  the  sawdust  into 
gaseous  products,  the  remaining  cavities  giving  the  burnt 
clay  a  porous  quality.  The  finished  product  should  be  hard 
and  should  give  a  metallic  sound  when  struck.  These  quali¬ 
ties  will  be  absent  if  the  terra  cotta  is  made  carelessly  or 
from  sandy  clays.  Porous  terra  cotta  will  resist  intense 
heat  and  will  therefore  act  as  a  protector  for  adjoining 
materials.  It  is  easily  workable;  that  is,  it  may  be  per¬ 
forated  with  nails  and  be  cut  with  a  saw  or  other  tools. 

71.  The  semiporous  terra  cotta,  used  mostly  in  the 
form  of  tiles,  is  made  from  a  mixture  of  fireclay  and  about 
20  per  cent,  of  coal  dust.  When  subjected  to  kiln  heat,  the 
coal  dust  will  assist  in  the  burning  of  the  tile  and  also  make 
it  partly  porous.  It  is  thought  that  this  variety  of  terra 
cotta  will  resist  fire  equally  as  well  as  porous  terra  cotta. 

72.  The  dense  terra  cotta  has  no  admixture  of  either 
coal  or  sawdust,  and  is  made  from  clay  alone;  it  is,  there¬ 
fore,  very  dense  and  of  a  high  crushing  strength.  Several 
clays,  such  as  fireclay  and  good  brick  clay  or  plastic  clay, 
are  used  in  its  manufacture.  Being  non-porous  and  gener¬ 
ally  having  a  glazed  surface,  it  is  a  good  protector  against 
moisture,  but  it  does  not  possess  the  fire-resisting  qualities 
of  the  preceding  varieties. 


38 


BUILDING  STONE  AND  BRICK 


§31 


SAND-LIME  BRICK 

73.  Methods  of  Manufacture. — The  composition  of 
sand-lime  brick  is  usually  94  per  cent,  of  sand  and  6  per 
cent,  of  slaked  lime.  This  mixture  is  forced  into  molds 
under  a  very  heavy  pressure,  and  the  brick  are  than  hardened 
by  means  of  superheated  steam.  These  brick  can  be  made 
in  many  colors  by  artificial  means,  and  can  thus  be  used  to 
effect  the  most  pronounced  designs. 

74.  There  are  several  methods  by  which  sand-lime  bricks 
are  manufactured.  In  the  Heuennekes  system,  the  lime 
is  burnt  in  a  kiln  and  crushed  into  a  fine  powder,  after  which, 
by  means  of  a  machine,  it  is  measured  into  definite  quantities- 
and  mixed  with  sand  that  has  previously  been  dried  and 
measured.  After  passing  through  another  machine,  which 
grinds  it  fine,  it  is  mixed  with  water  in  a  mixer,  whence  it 
is  transported  to  a  receptacle  where  the  lime  is  allowed  to 
slake  for  about  12  hours.  The  mixture  is  now  placed  in  a 
press,  which  forms  the  brick  under  a  pressure  of  about  5i  tons 
per  square  inch.  The  brick  are  then  transported  to  a  large 
steel  cylinder,  where  they  are  subjected  for  11  hours  to  chem¬ 
ically  charged  steam  acting  at  a  pressure  of  120  pounds  per 
square  inch,  when  the  brick  are  ready  for  use. 

75.  In  the  Schwarz  system,  the  sand  is  dried  under 
vacuum  in  a  preparing  machine,  after  which  the  lime  is  added 
and  thoroughly  mixed  with  the  sand  in  a  specially  constructed 
mixer.  The  subsequent  addition  of  carefully  measured  quan¬ 
tities  of  water  causes  the  lime  to  slake,  the  heat  evolved 
being  used  for  the  formation  of  silica  of  lime.  In  this  con¬ 
dition,  the  mixture  is  very  plastic  and  is  easily  molded  into 
brick  by  means  of  the  press.  The  brick  are  finally  subjected 
to  a  hardening  process  in  which  superheated  steam  is  used, 
and  are  thus  changed  chemically  into  calcium  silicate,  the 
hard  composition  of  the  brick. 

There  are  many  other  processes  of  sand-lime  brick  manu¬ 
facture,  more  or  less  patented,  but  they  all  have  the  essential 
features  of  the  processes  just  described.  * 


BUILDING  STONE  AND  BRICK 


39 


SIZE  AND  STRENGTH  OF  BRICK 

7(5.  Size  of  Brick. — There  is  no  standard  size  of  brick 
in  America.  The  dimensions  of  brick  vary  with  the  locality 
and  also  with  the  maker.  When  ordering  brick,  a  good  plan 
is  to  specify  that  all  brick  shall  be  over  a  certain  given  size; 
otherwise  it  will  be  found  that  many  more  brick  will  be 
required  for  a  job  than  was  at  first  expected.  Also,  as  brick 
are  often  laid  at  a  certain  price  per  thousand,  the  cost  per 
cubic  yard  of  masonry  will  be  increased  if  smaller  brick  than 
those  figured  on  are  used. 

In  the  New  England  States,  the  average  size  of  common 
brick  is  about  7f  in.  X  3f  in.  X  2t  in.;  New  York  and  New 
Jersey  brick  will  run  about  8  in.  X  4  in.  X  2i  in.;  and  the  walls 
laid  in  them  will  run  nominally  8,  12,  16,  and  20  inches  in  thick¬ 
ness  for  1,  If,  2,  and  2k  brick.  Most  of  the  western  com¬ 
mon  brick  measure  8i  in.  X  4i  in.  X  2k  in.,  and  the  thickness 
of  the  walls  measures  about  9,  13,  18,  and  22  inches  for 
thicknesses  of  1,  lk,  2,  and  2k  brick.  On  the  seacoast  of 
some  of  the  Southern  States,  the  brick  are  made  with  a  large 
percentage  of  sand,  and  will  average  9  in.  X  4k  in.  X  3  in. 

Most  manufacturers  of  pressed  brick  use  molds  of  the 
same  size;  hence,  pressed  brick  are  more  uniform  in  size. 
They  are  generally  8!  in.  X  4i  in.  X  2|  in.  Pressed  brick 
are  also  made  1^  inches  thick.  A  form  frequently  used  and 
known  as  Roman,  or  Pompeian,  brick  is  12  in.  X  4  in.  X  li  in. 
in  size.  In  order  that  a  good  bond  may  be  secured,  pressed 
brick  should  be  made  of  such  size  that  two  headers  and  a 
joint  will  equal  one  stretcher. 

The  weight  of  brick  varies  considerably  with  the  material 
used  in  their  manufacture  and  also  with  their  size.  Common 
brick  will  average  about  4k  pounds  each,  while  pressed  brick, 
owing  to  their  greater  density,  will  weigh  about  5  pounds  each. 

77.  Strength  of  Brick. — All  brick  should  be  of  uniform 
dimensions,  free  from  cracks,  pebbles,  or  pieces  of  lime,  and 
should  have  sharp  corners.  The  brick  should  be  well  burned, 
but  not  vitrified  so  that  they  become  brittle.  When  two 
211—9 


40 


BUILDING  STONE  AND  BRICK 


§31 


good  bricks  are  struck  together,  they  should  emit  a  metallic 
ring.  A  good  brick  will  not  absorb  over  10  per  cent,  of  its 
weight  of  water  if  allowed  to  soak  for  24  hours.  Brick  suit¬ 
able  for  piers  and  foundations  of  heavy  buildings  should  not 
break  under  a  crushing  load  of  less  than  4,000  pounds  per 
square  inch. 

The  bending  strength,  or  modulus  of  rupture,  of  a  brick 
is  quite  as  important  as  the  crushing  strength.  A  good  brick 
8  inches  long,  4  inches  wide,  and  2 %  inches  thick,  should  not 
break  under  a  center  load  of  less  than  1,600  pounds,  the  brick 
lying  flat,  supported  at  each  end  only,  and  having  a  clear 
span  of  6  inches  and  a  bearing  at  each  end  of  1  inch.  A 
first-class  brick  will  carry  2,250  pounds  in  the  center  without 
breaking,  and  a  brick  has  been  tested  to  9,700  pounds 
before  breaking. 

Table  VI  gives  the  average  ultimate,  or  breaking,  loads 
for  various  kinds  of  bricks. 


TABLE  VI 

STRENGTH  OF  BRICKS  AND  TERRA  COTTA 


Material 

Weight  per 
Cubic  Foot 

Pounds 

Compressive 

Strength 

Pounds  per 
Square  Inch 

Tensile 

Strength 

Pounds  per 
Square  Inch 

Modulus  of 
Rupture 

Pounds  per 
Square  Inch 

Soft,  inferior  brick . 

IOO 

I  .OOO 

40 

600 

Good,  common  brick . 

120 

10,000 

200 

600 

Best,  hard  brick . 

125 

12,000 

400 

800 

Paving  brick . 

130 

5,000 

Philadelphia  pressed  brick . 

150 

6,000 

200 

600 

Red  sand-lime  brick,  Arkansas  .  .  . 

no 

5,300 

Sand-lime  face  brick,  Maryland  .  . 

IOO 

3,500 

Light-gray  sand-lime  brick,  Iowa  .  . 

1 15 

4,800 

Light-gray  sand-lime  brick,  North 

Carolina . 

ii5 

5,100 

Terra  cotta . 

1 10 

5,000 

§31 


BUILDING  STONE  AND  BRICK 


41 


TABLE  Til 

STRENGTH  OF  BRICKWORK 

{Age,  6  Months ) 


Material 


Wire-cut  brick . 

Dry-pressed  brick . 

Dry-pressed  brick . 

Recompressed  brick . 

Light-hard,  sand-struck  brick  .  . 
Light-hard,  sand-struck  brick  .  . 
Hard,  sand-struck  brick  .  .  .  . 
Hard,  sand-struck  brick  .  .  .  . 

Hard,  sand-struck  brick  .  .  .  . 

Sand-lime  brick . 

Sand-lime  brick . 

Sand-lime  brick . 

Terra-cotta  work . 


Composition 
of  Mortar 

Parts 

Weight  per 

Cubic  Foot 

Pounds 

Compressive 

Strength 

Pounds  per 

Square  Inch 

i  cement,  5  sand 

136 

3,000 

1  cement,  5  sand 

137 

3,400 

1  cement,  1  lime, 

3  sand 

133 

2,300 

1  cement,  5  sand 

124 

1,700 

1  cement,  5  sand 

117 

1,900 

1  cement,  7  sand 

109 

853 

1  cement,  1  sand 

119 

2,100 

1  cement,  1  lime, 

3  sand 

1 13 

1,500 

1  cement,  5  sand 

108 

1,200 

1  cement,  3  sand 

112 

I ,  IOO 

i  lime,  3  sand 

108 

450 

neat  cement 

113 

1 ,400 

1 12 

2,000 

TABLE  Till 

ALLOWABLE  UNIT  STRESSES  FOR  BRICK  MASONRY 


Material 

Safe 

Compressive 

Strength 

Pounds  per 
Square  Inch 

Safe  Bending 
Strength 

Pounds  per 
Square  Inch 

1 

Brickwork,  laid  in  Portland-cement  mortar; 
cement  1,  sand  3 . 

250 

50 

Brickwork,  laid  in  natural-cement  mortar; 
cement  1,  sand  3 . 

150 

40 

Brickwork,  laid  in  lime-and-cement  mortar; 
cement  1,  lime  1,  sand  1 . 

125 

30 

Brickwork,  laid  in  lime  mortar;  lime  1,  sand  4 

IOO 

15 

42 


BUILDING  STONE  AND  BRICK 


§31 


Table  VII  gives  the  average  ultimate  strengths  for  brick¬ 
work  made  of  various  kinds  of  brick  set  in  mortar,  the  com¬ 
position  of  which  varies  from  cement  to  one  consisting  of 
1  part  of  cement  and  7  parts  of  sand.  The  values  given  in 
Table  VII,  being  ultimate  strengths,  have  to  be  used  in  con¬ 
nection  with  suitable  factors  of  safety.  The  usual  practice 
in  structural  and  architectural  engineering  is  to  use  the 
allowable  unit  values  for  brick  masonry  given  in  Table  VIII. 
These  values  are  considered  good  practice,  and,  in  most 
materials,  correspond  with  values  recommended  by  the 
building  laws  of  several  cities.  The  use  of  the  ultimate 
bending  strength,  or  modulus  of  rupture,  as  it  is  called, 
will  be  explained  in  a  subsequent  Section. 


STONE  CUTTING  AND  FINISHING 


STONE-CUTTING  TOOLS 

1.  Introduction. — Before  treating  of  stone  masonry, 
the  preliminary  work  of  dressing  the  stones  for  the  wall 
should  first  be  considered.  While  it  is  not  necessary  for  a 
structural  engineer  to  be  an  expert  stone  cutter,  he  should  be 
familiar  with  the  general  principles  of  the  art  in  order  to  be 
able  to  specify  the  proper  treatment  for  a  certain  class  of 
work  and  to  know  when  it  is  well  done. 

2.  Hammers. — In  Fig.  1  are  shown  the  various  hammers 
used  for  cutting  and  dressing  stone. 

The  double-faced  hammer,  shown  at  (a),  weighs  from 
20  to  30  pounds,  and  is  used  for  breaking  and  roughly 
shaping  the  stones  as  they  come  from  the  quarry. 

The  face  hammer,  shown  at  ( b ),  is  a  lighter  tool  than  the 
double-faced  hammer,  but  it  is  used  for  the  same  purposes 
when  less  weight  is  required.  It  has  one  blunt  and  one  cut¬ 
ting  end,  the  latter  being  used  for  roughly  dressing  the  stones 
preparatory  to  using  the  finer  tools. 

The  pick,  shown  at  (c),  is  used  for  coarsely  dressing  the 
softer  stones.  Its  length  is  from  15  to  24  inches,  and  the 
width  at  the  eye  is  about  2  inches. 

The  ax,  or  peen  hammer,  shown  at  (d) ,  is  about  10 
inches  long,  and  has  two  cutting  edges  about  4  inches  in 
length.  It  is  used  principally  for  making  drafts ,  or  margin 


COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS’  HALL,  LONDON 


2 


ELEMENTS  OF  STONE  MASONRY 


32 


lines,  around  the  edges  of  stones,  and  also  for  dressing  the 
faces,  being  used  after  the  point  and  before  the  patent 
hammer. 

The  tootli  ax,  shown  at  (e),  has  its  cutting  edges  a 
notched  to  form  teeth,  the  number  of  these  teeth  varying 


according  to  the  fineness  of  the  work.  It  is  used  for  roughing 
soft  stones  to  an  approximately  flat  surface  before  the  finish¬ 
ing  tool  is  used;  but  it  is  not  used  on  hard  stones,  like  granite 
and  marble,  as  the  points  would  become  dull  quickly  and 
need  constant  sharpening. 


§  32 


ELEMENTS  OF  STONE  MASONRY 


3 


The  bush  hammer,  shown  at  (/),  is  from  4  to  8  inches 
long,  with  ends  from  2  to  4  inches  on  a  side.  These  ends  are 
cut  into  a  number  of  pyramidal  points,  as  shown  at  a.  This 
kind  of  hammer  is  used  for  finishing  limestones  and  sand¬ 
stones  after  the  surfaces  have  been  made  nearly  even. 

The  crandall,  shown  at  (g),  consists  of  ten  or  twelve 
steel  bars  a  and  a  malleable-iron  handle  c.  In  the  end  of  the 
handle  is  a  slot  b,  in  which  the  bars  are  firmly  held  in  place 
by  a  key  d.  The  bars  are  made  of  ^-inch  steel,  are  about 
10  inches  long,  and  are  pointed  at  each  end,  as  shown.  The 
crandall  is  used  to  complete  the  finish  of  sandstone  after  the 
surface  has  been  partly  worked  with  a  tooth  ax  or  a  chisel. 


Fig.  2 


The  patent  hammer,  shown  at  (h),  is  made  of  from 
four  to  ten  thin  steel  blades.  These  blades  are  ground  to  an 
edge  and  are  held  together  by  means  of  bolts,  as  shown  at  b. 
This  hammer  is  used  to  finish  granite  or  hard  limestone.  The 
number  of  blades  required  to  give  the  proper  fineness  to  the 
cutting  is  usually  specified  as  four,  six,  eight,  or  ten  cut. 

The  hand  hammer,  shown  at  (i),  is  used  in  drilling  holes 
and  in  pointing  and  chiseling  the  harder  rocks.  It  is  about 
5  inches  in  length  and  weighs  from  2  to  5  pounds. 

The  mallet,  shown  at  (/),  is  used  in  cutting  the  softer 
stones.  It  is  made  of  wood,  the  head  being  about  7  or  8 
inches  in  diameter  and  5  or  6  inches  in  height. 


4 


ELEMENTS  OF  STONE  MASONRY 


§32 


3.  Chisels. — In  Fig.  2  are  shown  the  different  chisels 
used  for  dressing  stone. 

The  point,  shown  at  (a),  is  made  of  round  or  octagonal 
steel,  8  to  12  inches  long,  with  one  end  pointed.  It  is  used 
for  chipping  off  the  rough  faces  of  the  stone  and  reducing 
them  to  approximately  plane  surfaces,  ready  for  the  peen 
hammer,  and  also  to  give  a  rough  finish  to  stone  in  broached 
and  picked  work. 

The  tootli  chisel,  shown  at  (6),  is  used  only  on  soft 
stones,  serving  much  the  same  purpose  as  the  tooth  ax. 

The  drove  chisel,  shown  at  (c),  is  2  or  3  inches  wide  at 
the  end.  It  is  used  for  cutting  or  driving  the  rough  surfaces 
of  the  stone. 

The  pitching  chisel,  shown  at  (/),  is  used  for  making 
pitched-face  work. 

Other  forms  of  chisels  used  for  dressing  soft  stone  are  shown 
at  (d) ,  (e) ,  (g) ,  and  (k) . 

4.  Machine  Tools. — Besides  the  hand  tools  just 
described,  there  are  many  machine  tools  employed  to  pre¬ 
pare  the  stone  for  the  finer  treatment  to  be  given  by  hand 
work.  The  machine  tools  include  saws,  planers,  grinders,  and 
polishers. 

The  saws  used  for  cutting  stone  are  merely  thin  sheets  of 
steel,  the  edges  of  which  are  not  sharp.  There  are  three 
styles  of  stone-cutting  saws,  namely,  the  drag,  the  circular, 
and  the  band  saw.  The  drag  saw,  which  is  similar  in  shape 
to  the  ordinary  cross-cut  saw,  has  a  forward-and-backward 
movement  The  circular  saw,  as  the  name  implies,  is 
a  circular  disk  that  revolves  on  an  axis  through  its  center. 
The  band  saw  is  a  continuous  steel  band,  or  belt,  that  runs 
on  two  driving  wheels.  These  saws  are  aided  in  cutting  by 
feeding  sand  and  water  in  the  groove  that  is  being  made  in  the 
stone. 

The  planer  is  a  machine  used  in  reducing  the  inequalities 
in  rough  stone.  It  consists  of  a  table  that  moves  horizontally 
under  a  cutter,  the  stone  to  be  trimmed  being  fastened  on 
the  table  by  means  of  clamps. 


§32 


ELEMENTS  OF  STONE  MASONRY 


o 


The  grinder  and  the  poll  slier  are  practically  alike 
so  far  as  construction  is  concerned.  They  differ  only  in 
the  fineness  of  surface  they  are  capable  of  producing.  The 
machine  used  for  grinding  or  for  polishing  consists  principally 
of  a  circular  horizontal  table  on  which  the  stone  is  fastened, 
the  face  to  be  polished  being  always  turned  upwards.  This 
table,  with  the  stone,  revolves  about  a  vertical  axis  through 
its  center,  and  a  horizontal  metal  plate  that  can  be  moved  up 
and  down,  but  will  not  revolve,  is  pressed  on  the  stone.  Sand 
and  water  are  supplied  between  the  plate  and  the  stone, 
whose  surface  is  thus  abraded  until  the  proper  degree  of 
smoothness  is  attained. 


FIXISII  OF  STONEWORK 

5.  Stereotomy.- — The  science  of  making  patterns,  or 
templets,  to  which  a  stone  is  to  be  cut  to  fill  a  certain  place 
in  an  arch  or  other  complicated  piece  of  stonework,  is  called 
stereotomy.  In 
practice,  the  engineer 
makes  a  drawing  of 
the  intended  stone¬ 
work,  showing  where 
the  joints  in  the  face 
are  to  be  located,  and 
the  stone  cutter  then 
details  each  block  and 
cuts  it  to  fit  exactly 
with  the  others.  It 
is  therefore  impor¬ 
tant  for  the  engineer  to  understand  the  different  finishes  to 
which  stone  is  dressed,  but  it  is*  not  necessary  for  him  to  be 
able  to  make  the  templets  for  each  stone. 

6.  Rock-Faced  Work. — In  Fig.  3  is  shown  rock¬ 
faced,  or  pitcli-faeed,  work,  and  the  method  of  using  the 
pitching  chisel.  The  face  of  the  stone  is  left  rough,  just  as  it 
comes  from  the  quarry,  and  the  joints,  or  edges,  are  pitched 
off  to  a  line,  as  shown  at  a.  As  this  finish  requires  very  little 


Fig.  3 


6 


ELEMENTS  OF  STONE  MASONRY 


§32 


work,  rock-faced  dressing  is  cheaper  than  any  other  kind, 
especially  when  granite  or  hard  limestone  is  used. 

7.  Margins. — Building  stones  are  often  faced  an  inch 
or  so  from  their  edges.  This  dressed  strip,  shown  at  a,  Fig.  4, 
is  known  as  the  margin,  or  draft  line,  to  distinguish  it 
from  the  rock-faced  work  at  b.  This  margin  is  cut  on  soft 
stone  with  a  chisel,  but  on  extra -hard  stone,  such  as  granite, 
it  is  usually  cut  with  an  ax,  or  peen  hammer. 

8.  Pointed  Work. — In  producing  pointed  work,  a 

pointed  chisel  is  run  over  the  face  of  a  stone  to  knock  off  any 
large  projections.  This  work  is  called  rough-  or  fine-pointed 
work ,  according  to  the  number  of  times  the  work  is  gone  over. 
In  Fig.  5  is  shown  an  example  of  rough-pointed  work,  while 
in  Fig.  6  is  shown  an  example  of  fine-pointed  work  that  is  also 
margined. 

9.  Tooth-Chisel  Work.  —  The  finish  called  tootli- 
cliisel  work  is  produced  by  dressing  stone  with  a  tooth 

chisel.  The  surface  of 
a  stone  finished  in  this 
way  resembles  pointed 
work,  but  it  is  not  so 
regular.  Working 
stone  with  a  tooth 
chisel  is  one  of  the 
cheapest  methods  of 
stone  dressing  known. 

10.  Broached 

Fig-  4  Work. — Fig.  7  illus- 

»» 

trates  what  is  known  as  broached  work.  In  this  kind  of 
work  the  stone  is  dressed  with  a  point  so  as  to  leave  con¬ 
tinuous  grooves  over  the  surface.  At  a  is  shown  the  margin, 
or  draft  line,  and  at  b,  the  broached  center,  which  is  cut  in  two 
directions  in  order  to  illustrate  right-  and  left-hand  broaching. 

11.  Tooled  Work. — For  tooled  finish  a  tooth  chisel 
from  3  to  4^  inches  wide  is  used.  In  this  kind  of  work, 


Fig.  5 


Fig.  0 


7 


Fig.  7 


Fig.  8 


8 


Fig.  9 


Fig.  10 


9 


t 


Fig.  11 


Fig.  12 


10 


§32 


ELEMENTS  OF  STONE  MASONRY 


11 


the  lines  are  continued  across  the  width  of  the  stone  to  the 
draft  line  (when  one  is  used).  When  well  done,  tooled  work 
makes  a  very  good  finish  for  soft  stones. 

12.  Drove  Work. — The  finish  known  as  drove  work 
is  somewhat  similar  to  tooled  work,  but  it  is  generally  exe¬ 
cuted  on  harder  stone.  There  are  two  general  classes  of 
drove  work,  namely,  hand  drove  and  machine  drove ,  the  former 
being  shown  in  Fig.  8  and  the  latter  in  Fig.  9.  Machine-drove 
work,  as  will  be  noticed,  is  more  regular  than  hand  drove; 
also,  the  cuts  are  a  little  deeper,  although  this  is  hardly 
apparent  from  the  illustration.  For  a  large  quantity  of  cut¬ 
ting,  machine  work  is  cheaper  than  hand  work;  it  is  not  so 
pleasing  in  appearance,  however. 

13.  Crandalled  Work. — In  Fig.  10  is  shown  cran- 
d ailed  work,  which,  when  well  done,  gives  the  stone  a 
fine,  pebbly  appearance.  This  finish  is  especially  effective 
for  the  red  Potsdam  and  Longmeadow  sandstones.  In  the 
Eastern  States,  it  is  used  for  sandstones  probably  more  than 
any  other  finish. 

14.  Rubbed  Work. — In  producing  the  finish  known  as 
rubbed  work,  the  surfaces  of  stones  are  rubbed  with  a 
piece  of  softer  stone,  together  with  sand  and  water,  until  per¬ 
fectly  smooth.  Sandstones  and  most  of  the  limestones  are 
finished  in  this  manner,  and  if  granite,  limestone,  and  marble 
are  rubbed  long  enough,  they  will  take  a  beautiful  polish. 
The  operation  of  rubbing  can  be  performed  either  by  hand 
or  by  machine. 

If  the  rubbing  is  done  soon  after  the  stones  are  sawed  into 
slabs  and  are  still  soft,  it  is  cheaply  and  easily  performed,  as 
the  sawing  makes  the  face  of  the  stone  comparatively  smooth. 

15.  Bush-Hammered  Work. — In  Fig.  11  is  shown  the 
finish  of  a  stone  after  having  been  bush-hammered.  This 
finish,  which  leaves  the  surface  of  the  stone  full  of  points,  is  a 
very  attractive  one  for  hard  limestones  and  sandstones,  but 
should  not  be  used  in  dressing  the  softer  kinds. 


12 


Fig.  13 


ELEMENTS  OF  STONE  MASONRY 


13 


§ 


32 


16.  Patent-Hammered  Work. — A  stone  finished  by  a 
patent  hammer,  which  is  generally  used  on  granite  and 
hard  limestone,  is  shown  in  Fig.  12.  The  stone  is  first 
dressed  to  a  fairly  smooth  surface  with  the  point  and  then 
finished  with  the. patent  hammer.  The  degree  of  fineness  in 
the  finish  is  determined  by  the  number  of  blades  in  the 
hammer,  the  usual  number  being  eight  or  ten.  The  ax  may 
be  used  instead  of  the  hammer,  but  more  time  is  required  to 
obtain  an  equally  good  finish. 

17.  Vermiculated  Work. — In  Fig.  13  is  shown  a  stone 
having  a  somewhat  elaborate  finish,  which  is  known  as  ver¬ 
miculated  from  the  worm-eaten  appearance.  Stones  cut  in 
this  manner  are  used  principally  as  quoins,  or  corner  stones, 
and  in  base  courses.  Owing  to  the  cost,  this  style  of  dressing 
is  not  often  used  in  the  United  States. 

A  simple  method  of  obtaining  the  vermiculated  effect  is  by 
the  use  of  a  patented  sand-blast  process.  The  sand  employed 
in  this  process  is  carborundum  dust,  which  is  one  of  the 
hardest  substances  known.  It  is  blown  against  the  stone 
with  high  velocity  by  means  of  compressed  air.  While  this 
sand  will  rapidly  cut  and  wear  away  hard  surfaces,  such  as 
stone,  it  will  not  cut  soft,  yielding  surfaces,  because  the 
latter  do  not  suddenly  stop  its  motion,  but,  by  giving  way 
slightly,  permit  it  to  sink  in  a  short  distance  and  then  rebound. 
For  this  reason,  the  nozzle  of  the  blowing  machine  is  made  of 
soft  rubber  and  those  portions  of  the  stone  that  it  is  desired 
to  have  raised  are  covered  with  beeswax,  asphalt,  or  even 
heavy  paper.  The  remainder  of  the  face  of  the  stone  is 
eaten  away  by  the  sand  blast.  When  the  proper  depth  has 

been  reached,  the  sand  blast  is  stopped  and  the  material 

* 

used  to  cover  the  raised  part  of  the  stone  is  removed.  It  is 
then  necessary  to  put  on  a  few  finishing  touches  with  a 
pointed  chisel,  when  the  stone  is  ready  to  go  in  the  structure. 

The  sand  .blast  is  also  used  to  clean  stonework  that  has 
become  soiled  and  stained  by  smoke  and  dust. 

18.  Seale  Work. — A  pleasing  and  novel  method  of 
stone  dressing,  presenting  a  striking  effect  of  light  and  shade, 

211—10 


14 


ELEMENTS  OF  STONE  MASONRY 


§32 


is  illustrated  in  Fig.  14.  The  finish  shown  at  (a),  known  as 
scale  work,  is  obtained  by  cutting  out  rows  of  shallow 
flutes  between  the  drafts  of  the  stone  with  about  a  1-inch 


tool.  The  flutes  are  about  1  inch  wide,  and  are  alternated 
so  that  each  successive  course  “breaks  into”  the  preceding 
one  and  forms  with  it  a  series  of  hexagonal  hollows,  giving  a 
honeycombed  appearance.  The  application  of  this  finish  to 
a  window  jamb  is  shown  at  (b).  This  unique  method  is 


Fig.  15 


Fig.  16 


applicable,  of  course,  only  to  soft  stones,  such  as  limestone; 
but  to  these  it  gives  a  beautifully  crisp  and  varied  surface. 
The  cutting  can  be  done  either  by  hand  or  by  machinery. 


§32 


ELEMENTS  OF  STONE  MASONRY 


15 


19.  Rusticated  Work. — The  term  rusticated  work 
is  generally  used  to  designate  sunken  or  beveled  joints.  Two 
examples  of  this  finish  are  illustrated  in  Figs.  15  and  16,  the 
former  showing  the  stones  with  recesses  a  having  sharp 
edges  and  the  latter  with  recesses  a  having  rounded  edges. 
This  style  of  work  is  expensive,  and  is  usually  employed  in 
the  finish  of  basement  work  or  to  emphasize  piers  and  other 
projections. 


STONE  MASONRY 


GENERAL  CONSIDERATIONS 

20.  The  stonework  entering  into  the  construction  of  build¬ 
ings  may  be  divided  into  three  classes:  rubble ,  ashlar ,  and 
trimmings .  Before  describing  these,  however,  a  few  general 
observations,  applying  to  all  classes  of  stone  masonry,  are 
necessary. 

Whatever  may  be  the  quality  of  mortar  used,  the  wall  should 
contain  as  much  stone  and  as  little  mortar  as  possible,  as  the 
former  is  the  stronger  material.  In  rough  walling,  if  the 
stones  are  pressed  together  until  the  more  prominent  angles 
on  their  faces  come  almost  into  contact,  the  interstices  being 
filled  with  mortar,  there  results  better  work  than  if  a  thick, 
yielding  mass  of  mortar  is  allowed  to  remain  in  the  joints. 
Absolute  contact,  however,  is  not  advisable,  as  the  mortar  in 
drying  shrinks  and  may  leave  the  stones  bearing  only  on  the 
projecting  angles. 

The  joints  in  stonework  vary  in  thickness  from  ^  to  I 
inch.  A  *-inch  joint  is  probably  the  best  for  ordinary  work, 
while  a  h-inch  joint  should  be  used  for  rock-faced  work  only. 

21.  Stone  being  of  a  brittle  nature,  the  longer  pieces  in 
a  wall  must  be  properly  supported  and  well  bedded  in  order 
to  prevent  them  from  breaking.  It  is  also  best  to  avoid 
extremely  long  stones,  although  the  length  of  a  stone  should 
be  greater  than  its  height,  especially  in  ashlar  work,  on 


16 


ELEMENTS  OF  STONE  MASONRY 


§32 


account  of  the  vertical  bond.  There  is  a  certain  medium 
that  should  be  observed;  and  while  a  compact  mass,  broken 
as  little  as  possible,  is  most  desirable  in  stone  as  well  as  in 
brick  walls,  the  mason  will  often  find  it  better  to  break  a 

very  long  stone  into  two  or 
more  shorter  ones,  even  though 
by  so  doing  additional  joints  are 
made.  However,  in  laying  very 
long  stones,  as  in  steps  or  co¬ 
pings,  it  is  customary  to  bed 
them  only  at  the  ends,  so  that 
when  the  mortar  joint  shrinks 
there  will  be  no  danger  of  the 
stones  being  broken  by  bear¬ 
ing  on  some  obstruction  at  their 
middle. 

The  best  stones  should  be  used  for  piers,  jambs,  sills,  lintels, 
cornices,  band  courses,  etc.  in  the  order  mentioned;  and  all 
stones  in  which  the  length  of  the  face  is  greater  than  its 
height  should  be  so  quarried  that  they  can  be  laid  on  their 
natural  beds,  except,  of  course,  piers  and  long  jambs,  which 
necessarily  have  the  bed  of  the  rock  vertical. 


Fig.  17 


22.  Defective  Methods. — A  stone  with  a  hollow  cut 
in  it,  as  shown  at  a,  Fig.  17,  should  never  be  used  in  a  wall, 
because  when  the  mortar 
shrinks,  the  stone  will  bear  only 
at  the  edges  and  is  liable  to 
spall,  or  chip  off,  with  the  result 
shown  in  the  illustration.  If 
not  closely  watched,  careless  || 
stone  masons  are  tempted  to  cut 
stones  in  this  manner,  as  it  is 
much  easier  than  cutting  them 
to  a  true  bed. 

Another  improper  method 
often  carried  out  by  masons  is  to  cut  the  stone  as  shown  in 
Fig.  18  and  underpin  the  back  with  spalls.  This  practice  is 


§  32 


ELEMENTS  OF  STONE  MASONRY 


17 


also  liable  to  lead  to  disaster,  as  ]the  stone  may  split  as 
shown  at  a. 

On  account  of  the  liability  of  spalling,  as  illustrated  in 
Fig.  17,  rusticated  joints  are  often  used  in  the  basement  and 
first  story  of  tall  buildings. 


RUBBLE  WORK 

23.  Rubblework  consists  of  stones  in  which  the  adjoin¬ 
ing  sides  are  not  required  to  be  at  right  angles.  It  is  used  for 
rough  masonry,  as  in  foundations,  backing,  etc.,  and  fre¬ 
quently  consists  of  common  field  stone,  roughly  dressed;  but 
whenever  possible,  quarried  rubble  should  be  used,  as  better 
bedding  can  thus  be  secured.  Conglomerate  and  slate  stones 


Fig.  19 


abound  in  many  localities,  and  are  cheap  and  durable,  but 
they  do  not  cut  easily.  Such  stones  are  often  used  with 
good  effect,  however,  in  walls  with  cut-stone  or  brick  trim¬ 
mings;  or,  when  good  lengths  can  be  had,  they  are  used  for 
rock-faced  sills,  lintels,  and  trimmings. 


18 


ELEMENTS  OF  STONE  MASONRY 


§32 


24.  Rubble  Walls. — Fig.  19  illustrates  a  good  rubble 
wall,  the  stones  being  bonded  about  every  4  or  5  feet,  as. 
shown  at  a.  The  largest  and  best  stones  should  be  placed  at 


Fig.  20 

the  bottom  and  at  the  angles,  as  indicated  at  b,  and  should  be 
laid  up  in  alternate  courses  of  headers  and  stretchers.  Such 
work  is  generally  laid  with  beds  and  joints  dressed  but  very 


Fig.  21 

little,  the  rough  angles  only  being  knocked  off.  The  stones 
are  set  irregularly  in  the  wall  and  the  interstices  are  filled 
with  spalls  and  mortar.  If  better  work  is  desired,  the  joints 


H) 


ELEMENTS  OF  STONE 


MASONRY 


and  beds  of  the  stonework  should  be  hammer-dressed.  Such 
walls  arc  frequently  pointed  with  colored  mortar,  showing 
raised  joints. 

25.  Fig.  20  shows  a  form  of  rubble  masonry  much  used 
for  country  and  suburban  work.  The  quoins,  or  corner 
stones,  a  are  hammer-dressed  on  top  and  bottom,  and  may 
be  either  cut  stone  or  rock  face.  The  latter  finish  harmonizes 
well  when  stones  similarly  dressed  are  in  the  body  of  the  wall. 


Fig.  22 


All  joints  should  be  hammer-dressed,  as  shown  at  b ,  and  no 
spalls  should  show  on  the  face,  while  the  mortar  joints  should 
not  exceed  \  to  f  inch  in  thickness.  This  makes  an  effective 
wall,  especially  for  country  churches,  lodges,  and  other  small 
buildings;  but  the  work  is  expensive,  owing  to  the  labor 
required  in  dressing  the  joints. 

26.  Field-Stone  Walls. — In  Fig.  21  is  shown  a  field- 
stone  wall.  Walls  of  this  kind  are  built  of  small,  uncut 


20 


ELEMENTS  OF  STONE  MASONRY 


§32 


boulders,  and  are  frequently  employed  for  fences  and  rustic- 
house  work.  Such  walls  should  be  made  quite  thick  on 
account  of  the  round  and  unstable  shape  of  the  stones  used 
in  their  construction. 

27.  Walls  With  Brick  Quoins. — Fig.  22  shows  a  rub¬ 
ble  wall  with  brick  quoins,  or  corners,  at  a.  In  this  case, 
all  the  top  and  bottom  joints  of  the  rubblework  have  level 
beds ,  as  at  b.  This  kind  of  construction  makes  a  very  effect¬ 
ive  wall,  and  can  be  built  quite  cheaply  when  the  stone  used 
splits  readily,  or  can  be  laid  on  its  natural  bed,  thus' requiring 
but  little  dressing. 

28.  Coursed  Bubble. — In  walls  of  coursed  rubble, 

some  effort  is  made  to  produce  a  coursed  effect.  Stone  of  ran- 


Fig.  23 


dom  sizes  is  used,  but  little  or  no  attention  is  paid  to  uniform¬ 
ity  of  height  in  the  different  courses.  For  such  walls,  the 
stones  are  generally  roughly  dressed  before  the  wall  is  begun. 
Care  should  be  taken  to  get  as  nearly  parallel  beds  as  possible, 
and  to  bring  the  face  of  each  stone  to  a  fairly  even  surface  at 
approximately  right  angles  to  the  beds.  The  quoins  in 
coursed  rubble  are  usually  dressed  and  laid  with  more  care 
than  the  remainder  of  the  work ;  they  also  serve  as  gauge 


§32 


ELEMENTS  OF  STONE  MASONRY 


21 


courses.  Coursed  rubble,  when  well  built,  makes  a  very 
solid  wall  and  is  extensively  used. 

Fig.  23  illustrates  a  coursed  rubble  wall,  the  rubblework 
being  shown  at  a;  the  quoins,  at  b ;  the  bond  stones  running 
through  the  walls,  at  c;  and  two  of  the  course  joints,  at  d  e  f 
and  d'  e'  f. 


ASHLAR 


29.  Stonework  that  is  cut  on  four  sides  so  that  the 
adjoining  sides  will  be  at  right  angles  to  each  other,  is  known 
as  ashlar,  no  matter  whether  the  face  is  dressed  or  not. 


From  Fig.  23  it  is  evident  that  some  stones  of  this  form  are 
also  found  in  coursed  rubble.  The  latter  may  therefore  be 
considered  as  the  connecting  link  between  rubble  and  ashlar 
stonework. 

In  the  following  description  it  should  be  understood  that 
the  style  of  ashlar  designated  has  nothing  to  do  with  the 
finish  on  the  face  of  the  stone,  but  simply  the  manner  in  which 
it  is  laid,  although  certain  kinds  of  ashlar  are  generally  made 
with  the  styles  of  dressing  shown  in  the  illustrations. 

Ashlar  is  usually  laid  either  in  regular  courses  with  contin¬ 
uous  horizontal  joints,  as  shown  in  Figs.  24,  25,  and  26,  or  in 


22 


ELEMENTS  OF  STONE  MASONRY 


§ 


32 


broken  courses,  without  regard  to  continuity  of  the  joints,  as 
shown  in  Figs.  28  and  29.  All  ashlar  should  have  straight 
and  horizontal  bed  joints,  and  the  vertical  joints  should  be 
kept  plumb.  If  the  work  is  not  done  in  this  manner,  ashlar 
walls  will  present  a  poor  appearance. 

30.  Coursed  Aslilar. — A  class  of  stonework  in  which 
the  blocks  are  uniform  in  size  and  the  bed  joints  are  con¬ 
tinuous  is  known  as  coursed  aslilar.  When  such  stones 
can  be  obtained  readily,  this  kind  of  work  is  not  very 


Fig.  25 


expensive.  A  coursed-ashlar  wall  is  shown  in  Fig.  24,  in 
which  12"  X  36"  ashlar  is  shown  at  a,  and  the  backing,  which 
consists  of  12-inch  rubble,  at  b. 

31.  A  good  effect  is  produced  by  making  the  courses  of 
two  heights,  but  cut  in  regular  sizes,  and  having  the  vertical 
joints  in  alternate  courses  directly  over  one  another.  This 
class  of  work  is  illustrated  in  Fig.  25.  In  this  figure,  a  14-inch 
course  is  shown  at  a;  a  6-inch  course,  at  6;  and  the  backing, 
at  c.  The  latter  may  also  be  brick,  as  the  ashlar  can  be  well 
bonded  into  it.  If  the  narrow  band  course  b  is  rock-faced,  or 


§  32 


ELEMENTS  OF  STONE  MASONRY 


23 


has  some  different  finish  than  the  wide  courses  a,  the  appear¬ 
ance  of  the  work  will  be  further  improved. 

32.  The  stonework  of  many  public  and  office  buildings 

has  rustic  quoins  and  base  or  band  courses,  as  shown  in  Fig.  26. 

Here,  the  quoins,  which  have  a  1-inch  bevel,  or  chamfer,  at 

the  joints,  are  shown  at  a;  the  plain,  rubbed,  or  tooled  stones 

forming  the  face  of  the  wall,  at  b;  the  rustic  band  course, 

having  a  li-inch  chamfer  cut  on  it,  so  as  to  project  beyond  the 

quoins,  at  c ;  and  the  stone  or  brick  backing,  at  d.  This 

♦ 


Fig.  26 


method  of  construction  is  very  expensive,  owing  to  the  great 
amount  of  dressing  required. 

33.  Block-In-Course  Ashlar. — In  block-in-course, 
or  blocked-course,  ashlar  work,  all  blocks  of  stone  are 
cut  the  same  height  but  in  different  lengths,  and  no  attempt 
is  made  to  have  the  joints  come  over  one  another.  The 
length  on  the  face  is  usually  two  or  three  times  the  height, 
and  about  one-fifth  of  the  face  should  show  headers,  as  at  a, 
Fig.  27.  These  headers  should  rest  on  long  stretchers  below 
them,  in  order  that  the  wall  may  be  better  bonded.  As  a 


24 


ELEMENTS  OF  STONE  MASONRY 


rule,  this  style  of  work  looks  best  in  rock-faced  finish,  but  any 
finish  desired  may  be  used.  Many  quarries  have  stratified 


,»»YTT*-. 


■"  Vo".  y.  .  .  Y  ~ — 

1^0,  ^  {  \  v  - 

Sa>- 

>vsrjrt  ~ 


HH&WVf  _  a»  i  //•  ; J //,  ^n. 

-3?u<-  ,-A‘ 


.*^\ V  4,  ,\«i/ «»’ 

"Th  ;'.:'“iVtrv-  v  ••  • 


Fig.  27 

stone  that  is  just  the  proper  thickness  for  this  class  of  work, 
but  unless  the  stone  can  be  found  in  such  shape,  block-in¬ 
course  ashlar  work  is  generally  quite  expensive. 


Fig.  28 

34.  Random-Coursed  Ashlar. — The  method  of  laying 
random-coursed  ashlar  walls  is  illustrated  in  Fig.  28. 


§32 


ELEMENTS  OF  STONE  MASONRY 


25 


In  this  class  of  work,  no  attempt  is  made  to  have  the  vertical 
joints  over  one  another,  and  it  has  only  a  general  arrange¬ 
ment  in  courses,  as  shown. 

In  regard  to  the  best  methods  of  proportioning  the  blocks 
and  arranging  the  same  so  as  to  produce  a  harmonious  effect, 
it  is  first  necessary  to  consider  what  the  various  heights  of 
the  blocks  must  be  in  order  to  form  good  longitudinal  bond. 
Assume  the  lowest  height  at  4  inches — as  a  stone  any  thinner 
than  this  presents  an  appearance  of  weakness — and  the 
greatest  height  at  16  inches — as  any  higher  than  this  looks 
too  heavy  for  random-coursed  ashlar.  The  gradations 
may  then  be  4,  5,  6,  7,  8,  9,  10,  11,  12,  14,  and  16  inches, 


thus  giving  eleven  distinct  heights — a  variety  that,  when 
well  arranged,  produces  a  most  pleasing  effect. 

If  the  three  highest  numbers  are  taken  as  jumpers,  or  course 
levelers,  combinations  may  be  made  of  the  other  stones  so 
that  their  combined  thickness  will  equal  that  of  the  jumper. 
In  this  manner,  several  arrangements  are  possible. 

The  next  point  to  be  considered  is  the  lengths  of  the  blocks. 
The  bond,  or  the  lap  of  the  stones  over  one  another,  should 
be,  for  the  thinner  blocks,  at  least  6  inches,  and  for  the  thicker 
ones,  8  inches. 

35.  Broken  Ashlar. — In  broken-ashlar  stonework, 

no  attempt  is  made  to  have  the  stone  run  in  courses,  but 
each  block  is  cut  for  the  location  in  which  it  is  to  go.  It 


2G 


ELEMENTS  OF  STONE  MASONRY 


§  32 


generally  takes  more  time  to  build  broken  ashlar  than  coursed 
work;  hence  this  kind  of  wall  is  more  costly,  owing  to  the 
increased  amount  of  labor  required  to  fit  and  lay  the  dif¬ 
ferent  sizes  of  stone.  Broken  ashlar,  when  properly  executed, 
presents  a  pleasing  appearance.  It  is  generally  laid  up  as 
rock-faced  work,  but  in  some  cases,  it  is  tooled  or  hammer- 
dressed.  It  should  have  no  horizontal  joints  more  than 
4  feet  long,  and  several  sizes  of  stone  shotdd  be  used.  Fig.  29 
shows  an  ordinary  broken-ashlar  wall,  2  feet  thick,  the  sizes 
of  stones  used  being  4,  6,  8,  and  12  inches  in  height.  The 
quoins  are  shown  at  a,  and  the  body  of  the  wall  at  b. 

3G.  Best  Stone  for  Ashlar. — The  hardest  kinds  of 
rock  are  best  suited  for  ashlar  masonry,  as,  in  pitching,  the 
spalls  fly  off  more  easily  and  leave  the  fracture  in  sharp 
lines;  whereas,  with  the  softer  kinds  of  rock,  the  fracture  has 
a  bruised  and  crushed  appearance,  which  is  not  at  all  pleasing. 
The  best  stones  to  use  are  the  granites  and  the  most  compact 
b  luestones  and  sandstones. 

37.  Laying  Out  Ashlar. — If  ashlar  in  regular  courses 
and  sizes  is  to  be  used,  drawings  should  be  made  showing 
each  stone  of  different  size,  the  heights  of  the  courses,  and 
other  necessary  details.  The  drawings  for  public  and  office 
buildings  usually  show  every  stone,  unless  broken  ashlar  is 
used,  in  which  case  it  is  only  necessary  to  show  the  quoins 
and  jambs,  together  with  enough  of  the  ashlar  to  indicate 
the  character  of  the  work  desired.  It  is  almost  impossible 
to  follow  carefully  a  drawing  showing  all  the  stones  laid  as 
broken  ashlar. 

38.  Backing. — The  expense  of  ashlar  masonry  is  such 
that  it  is  commonly  used  merely  as  a  facing,  being  backed 
with  either  rubble,  masonry  or  brickwork.  It  is  only  on 
works  of  great  importance  and  solidity  that  ashlar  masonry  is 
used  throughout  the  whole  thickness  of  the  wall.  In  general, 
the  term  ashlar  applies* to  the  facing,  or  veneering,  of  stone, 
or  to  the  stones  that  constitute  the  facing. 


§  32  ELEMENTS  OF  STONE  MASONRY  27 

Both  stone  and  brick  are  used  as  backing,  but  in  most 
cases,  brick  is  the  cheaper  and  is  therefore  more  extensively 
employed.  When  using  brick  for  the  backing,  the  joints 
should  be  made  as  thin  as  possible,  employing  cement  mortar 
so  as  to  avoid  shrinkage.  Backing  of  this  kind,  however, 
should  never  be  less  than  8  inches  thick. 

When  a  hard,  laminated  stone  with  flat,  parallel  beds  can 
be  obtained,  it  should  be  used,  as  it  is  considered  to  be  a 
stronger  backing  than  brick.  Irregular  rubble  backing  should 
not  be  used  for  dwellings  higher  than  two  or  three  stories, 
unless  the  walls  are  made  at  least  one-fourth  thicker  than 


Fig.  30 


when  brick  backing  is  used.  All  backing,  whether  of  brick 
or  of  stone,  should  be  carried  up  at  the  same  time  and  built  in 
courses  of  the  same  thickness  as  the  ashlar.  This  kind  of 
construction  is  illustrated  at  a,  Fig.  30  (a)  and  ( b ). 

If  the  courses  are  not  over  12  inches  high,  they  are  usually 
bonded  sufficiently  to  the  backing  by  making  every  other 
course  wider,  and  by  having  one  through  bond  stone  to  every 
10  square  feet  of  wall,  as  shown  at  b,  Fig.  30  (a)  and  ( b ). 
This  method  is  called  a  toothed  bonding. 

39.  Method  of  Fastening  Thin  Ashlar. — Although 
not  so  strong  as  a  toothed  bond,  an  ashlar  facing  of  from  2  to  4 
inches  in  thickness  is  often  used,  especially  when  marble  or 


28 


ELEMENTS  OF  STONE  MASONRY 


§32 


other  expensive  stones  are  employed  in  the  construction.  In 
such  cases,  each  piece  of  ashlar  should  be  tied  to  the  backing 
by  at  least  one  iron  clamp ,  or  anchor ,  similar  to  that  shown 

>  iiirfife,  in  Fig.  31,  while  if  the 
stones  are  more  than 
3  feet  long,  two  an¬ 
chors  should  be  used. 
All  iron  clamps,  or  an¬ 
chors,  should  be  either 
galvanized  or  dipped 
Fig.  31  in  hot  tar  or  asphalt, 

to  prevent  the  formation  of  rust  on  them. 

Belt  courses  extending  8  inches  or  more  into  the  wall 
should  also  be  laid  about  every  6  feet  in  height,  so  as  to 
give  support  to  the  ashlar.  When  a  wall  is  faced  with  thin 
ashlar,  the  effective  bearing  strength  is  only  that  given  by 
the  thickness  of  the  brick  or  stone  backing,  the  facing  not 
being  relied  on  for  that  purpose. 


CARE  OF  STONEWORK 

40.  Pointing. — The  effects  of  the  weather  on  the 
exposed  edges  of  the  joints  in  masonry  usually  cause  the 
mortar  to  crumble  and  fall  out.  For  this  reason,  it  is  cus¬ 
tomary  to  refill  the  joints  to  a  depth  of  from  b  to  1  inch, 
with  specially  prepared  mortar.  This  operation  is  called 
pointing. 

In  work  that  is  to  be  pointed,  no  mortar  should  be  placed 
within  an  inch  of  the  front  edges  of  the  stone,  as  this  saves 
raking  out  the  joints  preparatory  to  pointing.  Sometimes, 
strips  of  wood  the  exact  thickness  of  the  joint  are  set  on  the 
edges  of  the  lower  course.  Then,  in  setting  the  stone,  the 
superfluous  mortar  is  pressed  out  and  the  stone  rests  on  the 
wooden  strips,  which  are  removed  when  the  mortar  is  hard. 

Pointing  is  generally  done  as  soon  as  the  walls  are  com¬ 
pleted,  but,  if  the  season  is  too  far  advanced,  it  should  be 
deferred  until  spring.  Under  no  circumstances  should  point- 


§32 


ELEMENTS  OF  STONE  MASONRY 


29 


ing  be  done  in  freezing  weather,  nor  in  extremely  hot  weather, 
as  then  the  mortar  will  dry  too  rapidly. 

The  most  durable  mortar  for  pointing  is  made  of  equal 
parts  of  Portland  cement  and  sand.  These  materials  are 
mixed  with  just  enough  water  to  give  a  plastic  consistency, 
and  to  this  mixture  are  added  a  little  slaked  lime  to  make 
the  mortar  stick  and  such  coloring  matter  as  may  be  desired. 

Portland  and  Rosendale  cements  discolor  most  limestones 
and  marbles,  and  some  sandstones.  However,  by  exercising 
care,  the  mortar  may  be  kept  from  the  face  of  the  stone,  and 
the  joints  may  be  pointed  afterwards  with  mortar  that  will 
not  stain.  A  cement  made  of  plaster  of  Paris,  lime,  and  mar¬ 
ble  dust,  called  Lafarge  cement ,  is  sometimes  used  for  setting 
marble  and  limestone;  it  is  claimed  that  this  cement  will  not 
cause  discoloration. 

41.  Cleaning. — After  pointing,  it  is  usually  necessary 
to  remove  the  mortar  stains,  etc.  from  the  face  of  the  wall. 
This  may  be  done  by  scrubbing  the  stonework  with  water 
containing  muriatic  acid,  the  proportions  being  about  20 
parts  of  water  to  1  part  of  acid.  For  cleaning  granite  and 
limestone,  wire  brushes  are  used,  and  for  sandstones  and 
other  soft  stones,  stiff  bristle  brushes  usually  serve  the  pur¬ 
pose.  The  stonework  should  be  scrubbed  until  all  mortar 
stains  are  removed. 

As  previously  stated,  the  sand  blast,  operated  by  either 
steam  or  compressed  air,  does  the  work  of  cleaning  walls  very 
effectively  and  rapidly.  It  not  only  removes  the  outer  layer 
of  the  discolored  stone,  but  leaves  a  fresh,  bright  surface. 
Even  fine  carvings  have  been  very  successfully  cleaned  by 
this  method. 

42.  Stone  Defects. — Granite  may  contain  cracks, 
black  or  white  lumps  known  as  knots ,  and  a  brownish  stain 
called  sap.  When  such  defects  are  found,  the  stone  should 
be  rejected,  provided  the  importance  of  the  work  justifies  it. 
Cracks  are  the  main  things  to  guard  against,  however,  and 
they  may  be  detected  by  the  absence  of  the  clear  ringing 
sound  when  the  stone  is  struck  with  a  hammer. 


211—11 


30 


ELEMENTS  OF  STONE  MASONRY 


§32 


Sand  holes  are  frequently  found  in  sandstones.  These  are 
bodies  of  uncemented  sand,  that  become  dislodged  by  jarring 
or  by  the  action  of  water,  and  produce  a  pitted  appearance 
and  an  uneven  color.  Attention  must  also  be  paid  to  secur¬ 
ing  uniformity  of  color,  as  sandstone  from  different  parts  of 

the  same  quarry  may  vary  greatly  in  this  respect. 

• 

43.  Faults  in  Dressing  Stone. — The  common  faults 
of  cut  stone  are  coarseness  and  poor  workmanship.  In  dress¬ 
ing  stone,  builders  will  avoid  any  work  beyond  that  necessary 
to  make  the  material  barely  acceptable  to  the  inspector. 

Frequently,  the  ends  of  cornices,  belt  courses,  etc.  will  not 
match  properly.  It  should  be  strictly  required  that  the 
utmost  care  be  taken  in  cutting  all  similar  pieces  to  the  same 
pattern,  and  that  the  abutting  surfaces  be  closely  dressed. 

44.  Laying  of  Stonework.— In  erecting  stonework, 
care  should  be  exercised  to  have  the  stone  set  on  the  natural 
bed,  with  good  joints,  and  not  in  too  small  nor  in  too  thin 
pieces.  The  bed  joints  in  ashlar  work  should  be  square  to 
the  face  of  the  work,  and  not  less  than  4  inches  wide  at  both 
top  and  bottom.  The  proper  bonding  of  the  wTalls,  especially 
for  the  ashlar  and  for  the  trimmings,  should  be  given  very 
careful  attention,  as  should  also  the  placing  of  lintels,  copings, 
wall  anchors,  etc. 

Another  point  that  requires  attention  is  the  formation  of 
the  joints  on  which  great  pressure  comes;  also,  the  mortar 
should  be  kept  back  from  the  face,  so  that  the  edges  of  the 
stones  will  not  be  chipped  off.  In  pointing,  the  joints  should 
be  well  raked  out  and  the  pointing  mortar  properly  laid. 
Many  other  precautions  for  the  good  performance  of  the 
work  will  doubtless  suggest  themselves  to  the  careful 
superintendent'. 


§32 


ELEMENTS  OF  STONE  MASONRY 


31 


TRIMMINGS 


SPECIAL  STONES 

45.  The  term  trimmings,  as  generally  used,  includes 
moldings,  belt  course,  sills,  caps,  and  other  cut  stone  (except 
ashlar)  used  for  ornamental  purposes. 

The  stones  for  such  work  should  be  of  good  quality,  having 
the  beds  closely  dressed  and  the  ends  square  and  properly 
matched.  The  faces  may  be  pitched  off,  but  all  washes, 
soffits,  etc.  should  be  cut  or  rubbed.  When  a  brick  building 
is  trimmed  with  stone,  great  care  should  be  taken  to  have  the 
trimmings  set  properly,  so  that  it  will  not  be  necessary  to 
split  the  courses  of  brick  below  or  above,  for  such  a  procedure 
will  spoil  the  appearance  of  the  building. 

46.  Bond  Stones  and  Templets. — All  piers  above  a 
certain  size  require  bond  stones,  that  is,  stones  the  full  size 
of  the  pier,  to  prevent  them  from  splitting.  The  course  of 
brick  placed  underneath  should  be  brought  to  an  exact  level 
to  receive  the  stone;  otherwise,  the  weight  above  may  cause 
it  to  crack  or  become  displaced.  Only  strong  stones,  such  as 
granite,  bluestone,  and  hard  trap  rock,  should  be  used,  and 
they  should  be  cut  to  the  full  size  of  the  pier. 

47.  Bearing  stones  placed  under  the  ends  of  beams 
and  girders  to  distribute  the  weight  more  evenly  on  the 
wall  are  called  templets.  The  pressure  per  square  inch 
allowed  on  the  brickwork  or  stonework  in  the  wall  under 
the  templet,  as  specified  by  the  building  laws  of  the  town 
in  which  the  building  is  being  erected,  governs  the  size  of 
the  templet  required,  and  is  usually  from  100  to  200  pounds. 
It  is  better,  however,  to  make  templets  too  large  rather 
than  too  small.  A  hard,  tough  stone  should  always  be 
employed,  and  the  usual  rule  is  that  the  thickness  of  the 
stone  should  be  one-third  of  the  smallest  surface  dimension, 
except  when  very  large  stones  are  used;  but  the  least  thick¬ 
ness  should  be  4  inches.  When  a  wooden  girder  rests  on  a 


32 


ELEMENTS  OF  STONE  MASONRY 


§32 

templet,  a  good  plan  is  to  place  a  flat  stone  above  the  end  of 
the  girder,  so  that  the  wall  will  rest  on  the  stone  and  not  on 
the  wood.  This  is  advisable  for  the  reason  that  when  the 
wood  shrinks  the  settlement  may  cause  cracks  in  the  wall. 

Strictly  construed,  bond  stones  and  templets  are  not  ashlar; 
but  as  they  require  more  or  less  dressing,  they  are  considered 
as  being  ashlar. 

48.  Quoins. — The  corner  stones  of  a  wall,  as  already 
inferred,  are  known  as  quoins.  They  are  often  dressed 


differently  from  the  other  stones  in  order  to  make  them  more 
prominent.  Quoin  stones  should  always  be  equal  in  size  to 
the  largest  stone  used  in  the  wall;  otherwise,  the  effect  of 
strength  and  solidity  that  they  are  intended  to  produce  will 
be  lost.  Sometimes,  the  quoins  of  a  rubble-stone  wall  are 
built  of  brick. 

49.  Jamb  Stones. — The  stones  used  in  the  sides  of  a 
door  or  window  opening  are  called  jamb  stones.  The 
alternate  ones  should  extend  through  the  width  of  the  wall  to 


§32 


. ELEMENTS  OF  STONE  MASONRY 


33 


insure  a  good  bond.  Fig.  32  illustrates  cut-stone  jambs  in  a 
rubble  wall.  The  jamb  stones  bonding  into  the  wall  trans¬ 
versely  are  shown  at  a;  those  bonding  longitudinally,  at  b\ 
the  stone  window  sill,  at  c\  and  the  rubble  wall,  at  d. 


Fig.  33  Fig.  34 


50.  Occasionally,  when  stone  piers  or  pilasters  are  built 
on  the  outside  of  the  building,  the  windows  are  recessed  so 
that  the  projection  of  the  sills  and  lintels  will  not  be  so 


i 


iSSfe, 


ilMMl 


if## 


noticeable.  This  is  illustrated  in  Fig.  33,  in  which  a  shows  the 
lintel;  b ,  the  sash ;  and  c,  one  of  the  jamb  stones. 

Jambs  and  quoins  are  often  finished  with  a  draft,  or  angle, 
linel  especially  when  the  softer  stones  are  used.  Fig.  34 


34 


ELEMENTS  OF  STONE  MASONRY 


§32 


illustrates  this  method  of  finishing,  the  quoin  or  jamb  stone, 
as  the  case  may  be,  being  shown  at  a;  the  angle  draft,  at  b\ 
and  the  broken  ashlar  wall,  at  c. 

51.  Washes  and  Drips. — The  tops  of  all  cornices, 
belt  courses,  etc.  should  have  an  outward  and  a  downward 

pitch  from  the  walls,  as  shown 
at  b,  Fig.  35.  If  the  top  is 
level  or  slopes  inwards,  rain 
will  collect,  and  in  time  will 
cause  the  disintegration  of 
the  mortar  in  the  adjacent 
joints  and  finally  penetrate 
the  wTall.  The  beveled  sur¬ 
faces  are  called  washes. 
On  the  under  side  of  the  cor¬ 
nices,  etc.,  drips  should  be 
made,  to  prevent  rain  water 
from  flowing  down  the  face 
of  the  wall.  At  a,  Fig.  35, 
is  shown  the  drip;  at  5,  the 
wash  of  the  cornice;  and  at  c ,  the  stone  cut  to  a  sharp  angle, 
so  as  to  shed  part  of  the  water  from  that  edge. 

Window  sills  should  also  have  a  drip  cut  in  them,  as  shown 
at  a,  Fig.  36,  so  as  to  keep  the  walls  below  from  becoming  dis¬ 
colored  by  dirt  washed  off  the  sills  by  rain. 


LINTELS 

52.  A  lintel,  often  called  a  cap ,  is  a  stone  that  supports 
the  wall  over  a  door  or  a  window  opening;  and,  as  it  must 
resist  bending  stress,  it  should  be  a  strong,  tough  stone  having 
an  ample  cross-section.  The  ends  of  stone  lintels  should  not 
be  built  into  the  walls  more  than  is  necessary  to  give  -sufficient 
bearing;  4  to  6  inches  at  each  end  is  the  usual  allowance. 
There  should  be  a  little  play  allowed  at  each  end,  so  that  the 
lintels  can  yield  slightly  without  cracking  if  the  walls  on  either 
side  settle  unevenly. 


ELEMENTS  OF  STONE  MASONRY 


35 


§32 

53.  Relieving  Lintels. — Often,  when  a  long  lintel  is 
used  over  an  opening,  the  stonework  above  the  lintel  is 
arranged  as  illustrated  in  Fig.  37,  in  which  a  shows  the  lintel, 
and  b  the  relieving  lintel,  or  stone  above  it  cut  with 


c  c 

1  ~1 

1 

Pig.  37 

two  diagonal  joints,  as  at  c.  In  this  way,  some  of  the  load  is 
taken  off  the  lintel  and  transferred  to  the  wall  on  both  sides 
of  the  opening. 

When  a  lintel  extends  through  the  wall  and  is  not  sup¬ 
ported  by  angles  or  beams,  the  strength  may  be  increased, 
provided  the  stone  is  stratified,  by  cutting  it  in  such  a  manner 


that  the  layers  will  set  on  edge,  as  shown  at  a,  Fig.  38.  This 
procedure,  however,  may  cause  the  face  of  the  lintel  to  flake 
off  if  the  layers  of  stratification  are  thin  and  not  securely 
joined  together. 


36 


ELEMENTS  OF  STONE  MASONRY 


§32 


54.  When  considerable  weight  rests  on  a  stone  lintel,  a 
brick  relieving  arch  may  be  used;  but  unless  much  skill  is 
exercised  in  its  construction,  this  arch  will  detract  from  the 

appearance  of  the  building,  especially  if 
it  extends  through  the  entire  thickness  of 
the  wall.  To  avoid  this  result,  if  stone  of 
sufficient  depth  cannot  be  used,  the  lintel 
may  be  strengthened  by  the  use  of  iron 
beams  or  angles.  When  the  lintel  is  of 
moderate  length,  it  is  sufficient  to  use  a 
piece  of  angle  iron,  as  in  Fig.  39,  in  which 
a  shows  the  stone  lintel;  b,  the  angle, 
which  should  have  its  longer  side 
vertical ;  c,  a  wooden  beam  to  which 
the  interior  woodwork  is  nailed;  d,  the 
brick  wall;  and  e ,  the  window  reveal, 
or  side. 


55.  I-Beam  Supports. — When  the  width  of  the  opening 
is  considerable,  stone  lintels  should  be  supported  on  I  beams. 


Fig.  40 


e 


Fig.  41 


If  only  the  weight  of  the  lintel  and  wall  is  to  be  carried,  a 
single  I  beam  may  be  used,  as  shown  in  Fig.  40,  in  which  the 


§32 


ELEMENTS  OF  STONE  MASONRY 


37 


stone  lintel  is  shown  at  a;  the  I  beam,  at  b ;  the  wooden  beam 
to  which  the  wood  finish  is  attached,  at  c\  the  reveal,  at  d\ 
and  the  brick  wall,  at  e. 

If,  in  addition  to  the  walls,  the  floorbeams  over  openings 
must  be  carried,  it  is  best  to  use  two  I  beams,  as  in  Fig.  41. 
Here,  the  stone  lintel  is  shown  at  a;  the  I  beams,  held  together 
by  bolts  and  separators,  at  b\  an  iron  plate  on  which  the  wall 
rests,  at  c\  a  floorbeam,  at  d;  the  window  reveal,  at  e\  and  the 
brick  wall,  at  /. 

When  it  can  be  avoided,  the  best  plan  is  not  to  support  the 
weight  of  a  wall  on  both  stone  and  steel  or  wooden  beams, 
as  the  deflection  of  each  material  is  different,  making  it  prac¬ 
tically  impossible  for  each  to  carry  its  proper  share  of  the 
load.  The  weight  should  preferably  be  borne  by  the  steel 
beams  alone. 


56.  Built-Up  Lintels. — It  is  sometimes  necessary  to 
use  a  stone  lintel  that  is  10  or  12  feet  long.  Since  it  is  difficult 
to  obtain  a  single  piece  of  stone  of  this  length,  the  lintel  may 


be  made  in  sections,  as  in  Fig.  42.  At  least  three  stones 
should  be  used,  and  the  joints  should  be  cut  as  shown  at  a. 
When  cut  in  this  manner,  the  stones  are  self-supporting. 
The  end  pieces  may  be  built  into  the  wall  for  a  considerable 
length,  so  as  to  act  as  cantilevers  supporting  the  middle  sec¬ 
tion.  If  such  long  lintels  are  used,  however,  it  is  better  to 
carry  them  on  I  beams,  as  shown  in  Figs.  40  and  41. 

In  stonework  it  is  best  to  avoid  placing  a  pier  directly  on 
top  of  the  lintel;  all  openings  should  preferably  be  directly 
above  one  another. 


38 


ELEMENTS  OF  STONE  MASONRY 


§32 


SILLS 

57.  Lug  and  Slip  Sills. — In  masonwork,  sill  is  the 
name  given  to  the  stones  that  form  the  bottom  of  the  win¬ 
dow  and  door  openings  in  stone  or  brick  walls. 

Lug  sills  have  flat  ends,  or  lugs,  built  into  the  wall. 
These  lugs  should  not  enter  the  walls  a  distance  of  more  than 
4  inches,  and  should  be  bedded  on  mortar  only  at  the  ends. 
If  a  sill  is  bedded  solid  and  settlement  occurs,  it  will  probably 
be  fractured  at  the  jamb  line,  as  the  pier  or  side  walls  will 
likely  settle  more  than  the  wall  under  the  opening.  The 


joints  under  the  sills  should  be  filled  when  the  finished  walls 
are  cleaned  down. 

Slip  sills  are  made  just  the  width  of  the  opening,  and 
are  not  built  into  the  walls,  being  put  in  place  after  the  frame 
is  set.  Such  sills  are  cheaper,  but  they  do  not  look  so  well  as 
lug  sills;  besides,  there  are  exposed  vertical  joints  at  the  ends 
into  which  water  will  penetrate.  However,  any  settlement 
of  the  masonry  is  not  liable  to  break  a  slip  sill,  and  they  arc 
therefore  often  used  in  the  lower  parts  of  heavy  buildings. 


§32 


ELEMENTS  OF  STONE  MASONRY 


39 


58.  All  sills  should  have  a  bevel,  or  wash,  about  1  inch 
to  the  foot,  extending  to  the  back  of  the  reveal,  as  shown  in 
Fig.  43.  They  sometimes  have  a  beveled  surface  the  full 
length  of  the  sill,  the  brickwork  being  made  to  fit  the  stone. 
The  latter  construction,  however,  is  not  good  practice,  as  it 
permits  water  running  down  the  jamb  to  enter  the  joint  between 
the  brick  and  the  stone ;  the  sloping  upper  face  also  forms  an 
insecure  bearing  for  the  wall  resting  on  it.  In  Fig.  43  is 
shown  the  proper  method  of  cutting  the  surfaces.  As  shown 
at  a,  the  flat  end  of  the  lug  sill  carries  the  brickwork  reveal  c. 
At  b  is  shown  the  bevel,  or  wash,  and  at  d,  the  drip. 


COPING 


59.  If  no  cover  is  put  on  the  top  of  a  wall,  rain  will  wash 
out  the  joints.  For  this  reason,  parapet  walls  are  capped 


Fig.  44 


with  a  wide  stone  called  coping.  Terra  cotta  is  also  occa¬ 
sionally  used  for  this  purpose.  The  upper  surface  of  the 
coping  should  be  pitched,  as  shown  at  a,  Fig.  44,  and  should 
have  a  drip  on  the  under  side,  as  shown  at  b.  The  coping 
should  be  about  3  or  4  inches  wider  than  the  wall.  Hori¬ 
zontal  coping  stones  are  often  clamped  together  at  their  ends 
to  prevent  them  from  becoming  displaced. 


40 


ELEMENTS  OF  STONE  MASONRY 


§32 


Gable  copings  should  be  anchored  either  by  bond  stones 
or  by  long  iron  ties.  A  form  of  coping  that  is  extensively 


used  is  shown  in  Fig.  45,  in  which  the  coping  is  shown  at  a, 
and  the  corbel,  at  c.  The  bottom  stone  b ,  sometimes  known 


as  the  kneeler,  should  always  be  well  bonded  into  the  wall. 
In  some  cases,  the  coping  is  cut  in  steps,  so  that  each  stone 


§32 


ELEMENTS  OF  STONE  MASONRY 


41 


will  have  a  horizontal  bearing  on  the  wall.  This  method  of 
coping  is  objectionable,  however,  on  account  of  the  increased 
number  of  joints.  It  is  well  to  have  long  pieces  of  coping, 
so  as  to  reduce  the  number  of  joints — a  common  length  is 
6  feet.  A  short  piece  of  coping  cut  as  shown  at  a,  Fig.  46, 
should  be  inserted  at  intervals  to  bond  the  coping  securely  to 
the  wall. 

Gable  copings  do  not  necessarily  have  to  be  pitched  on 
top,  but  they  should  project  on  both  sides  of  the  wall  and 
should  have  a  drip  at  each  edge  so  as  to  shed  rain  water. 


STONE  STEPS 


60.  In  laying  stone  steps,  it  is  important  to  see  that 
they  are  firmly  supported  at  each  end,  but  left  free  in  the 
middle.  If  the  stones  forming  the  steps  have  a  bearing  along 


Fig.  47 


their  entire  length,  they  might,  after  a  slight  settlement  in  the 
foundations,  rock  from  side  to  side  when  stepped  upon,  or 
they  might  crack.  In  order  to  strengthen  extra  long  steps, 
however,  it  is  sometimes  necessary  to  insert  a  middle  bearing; 
great  care  must  then  be  taken  to  have  the  middle  and  two 
end  supports  exactly  on  a  line.  Each  step  should  overlap 
the  one  below  at  least  \\  inches,  and  should  have  an  outward 
pitch  of  about  -§-  inch.  Steps  having  a  nosing,  as  shown  at  a, 
Fig.  47,  make  a  good  appearance,  but  they  are  more  expensive 
than  the  ordinary  steps. 


42 


ELEMENTS  OF  STONE  MASONRY 


§32 


A  hard  stone,  such  as  granite  or  bluestone,  should  be 
used  for  steps;  but  for  private  residences,  where  the  wear 
is  not  great,  limestone  or  a  fairly  hard  sandstone  may  be 
employed. 

61.  Stone  stairs  are  sometimes  made  wTith  only  one  end 
supported.  This  end  is  built  solidly  into  the  wall,  and  each 
step  is  carried  on  the  next  lower  one,  as  illustrated  in  Fig.  48. 
As  shown  at  a,  the  landing  is  rabbeted  into  the  tread  of  the 
top  step.  The  manner  in  which  each  step  is  cut  and  supported 
by  the  lower  one  is  shown  at  b.  To  be  safe,  the  bearing 
dimensions  should  not  be  less  than  are  indicated  in  the  illus¬ 
tration.  The  bottom  step  should  be  firmly  held  in  place  by 


1 


Fig.  48 

dowels  set  into  the  floor,  as  shown  at  c,  as  this  step  must 
sustain  the  thrust  of  the  whole  flight.-  The  stone  blocks 
forming  the  steps  are  usually  cut  in  the  triangular  cross- 
section  shown,  which  method  of  cutting  gives  a  good  appear¬ 
ance  to  the  soffit,  or  ramp,  of  the  stairs. 

62.  Iron  staircases  are  extensively  used  in  fireproof 
construction.  In  such  cases,  the  treads,  and  sometimes  the 
risers,  consist  of  marble  slabs,  while  slate,  which  is  cheaper, 
is  also  used.  Staircase  railings  for  stairways  having  stone  or 
iron  steps  are  often  elaborately  finished.  They  are  generally 
made  of  iron,  which  is  doweled  into  the  ends  of  the  steps. 


§  32 


ELEMENTS  OF  STONE  MASONRY 


43 


FOOTINGS 


PURPOSE  OF  FOOTINGS 

63.  If  a  man  stands  on  soft  mud,  marshy  ground,  or 
quicksand,  he  sinks  to  a  greater  or  less  depth,  proportional 
to  his  weight.  If,  however,  he  stands  on  a  plank  or  a  wooden 
platform,  or  on  a  post  or  posts  driven  through  the  mud  or 
marsh  to  firmer  ground,  his  weight  is  distributed  over  a 
larger  area  in  the  first  case  and  carried  down  to  a  better 
foundation  in  the  second. 

The  same  thing  is  true  of  the  footings  of  buildings. 
By  spreading  the  load,  or  weight  of  the  structure,  over  a 
larger  area  or  bearing  surface,  the  weight  of  the  building  is 
more  evenly  distributed,  and  the  likelihood  of  a  settlement, 
due  to  compression  of  the  ground,  is  greatly  diminished. 
For  this  reason,  the  higher  and  heavier  the  building  is  to  be, 
the  wider  and  deeper  the  supports  or  footings  for  the  founda¬ 
tion  must  be;  and  if  extremely  soft  or  yielding  ground  is 
encountered,  piling  should  be  resorted  to  in  order  to  carry  the 
weight  of  the  building  to  a  more  solid  base. 

64.  Footings  may  be  of  iron,  timber,  or  large,  flat  build¬ 
ing  stones- laid  directly  on  the  ground  or  on  a  bed  of  concrete, 
or  they  may  be  of  concrete  alone  or  with  reinforcement,  or  of 
concrete  and  stepped-up  brickwork.  Where  piling  is  used, 
heavy  capping  timbers  are  often  placed  on  the  heads  of  the 
piles,  with  either  stone  or  concrete  footings  resting  on  them; 
or  large  footing  stones  may  be  laid  directly  on  the  piles. 


TIMBER  FOOTINGS 

65.  Timber  is  often  used  for  footing  courses  where  a 
large  bearing  surface  is  necessary  and  can  be  obtained,  pro¬ 
vided,  always,  that  the  timber  can  be  kept  from  rotting.  In 
some  cases,  the  timber  is  charred  on  the  outside;  and,  again, 
it  is  coated  with  asphalt.  If  the  ground  is  continually  wet, 
there  is  little  to  fear,  as  timber  will  not  decay  when  kept  con- 


44 


ELEMENTS  OF  STONE  MASONRY 


§32 


stantly  saturated  with  water;  but  when  alternately  wet  and 
dry,  unprepared  timber  cannot  be  depended  on. 

A  good  method  of  placing  planks  under  walls  for  foot¬ 
ings  is  to  use  3"  X  1 2"  plank  cut  in  short  lengths  and  laid 
crosswise  in  the  trench.  A  layer  of  plank  of  the  same  size 
is  then  laid  lengthwise,  followed  by  a  third  layer  placed 
transversely.  In  Fig.  49,  the  stone  footing  b  rests  on  the 


Fig.  49 


footing  planks  a  and  carries  the  stone  foundation  wall  c 
between  the  sides  d  of  the  trench. 


CONCRETE  AND  STONE  FOOTINGS 

66.  Fig.  50  shows  a  20-inch  brick  wall  b  erected  on  a  con¬ 
crete  footing  a  that  is  20  inches  thick  and  36  inches  wide. 
Figs.  51  and  52  show  concrete  bases  a  and  stepped-up  brick 
footing  courses  b.  In  Fig.  51,  each  step  of  brickwork  is  set 
back  2  inches  for  each  course,  while  in  Fig.  52,  each  step  is  set 
back  4  inches  for  each  two  courses.  At  c  is  shown  a  20-inch 
brick  foundation  wall  resting  on  the  stepped-up  brick  footing. 

Fig.  53  illustrates  a  stone  footing  a,  composed  of  three 
courses  of  flat  stone,  each  course  being  8  inches  thick.  The 
top  course  projects  6  inches  on  each  side  of  the  20-inch  brick 
foundation  wall  b,  and  the  middle  and  bottom  -courses  each 
project  3  inches  making  the  width  of  the  bottom  stone  3  feet 
8  inches. 


§  32 


ELEMENTS  OF  STONE  MASONRY 


45 


Fig.  54  shows  a  stepped-stone  footing  a  similar  to  that 
shown  in  Fig.  53,  but  supporting  a  24-inch  stone  foundation 


wmm 


Fig.  50 


Fig.  51 


wall  b.  Each  base  course  advances  3  inches  beyond  the  one 
above. 


W&MMM 


'■lav- 


1 

Fig.  52 


Fig.  53 


Fig.  55  shows  a  footing  consisting  of  a  single  course  of 
stone  a,  8  inches  thick  and  28  inches  wide,  carrying  the 
stone  wall  b,  20  inches  thick. 

211  —  12 


46 


ELEMENTS  OF  STONE  MASONRY 


§32 


67.  As  a  rule,  concrete,  when  of  sufficient  depth  and 
width,  and  when  properly  made  and  laid,  makes  the  best 
footing  course.  Concrete  for  footings  should  be  made  of 


Fig.  54 


Fig.  55 


1  part  of  good  cement,  3  parts  of  clean,  sharp  sand,  and 
6  parts  of  sharp,  broken  stone.  In  very  important  work, 
such  as  bridge  piers  and  the  footings  of  very  tall  buildings, 
chimneys,  etc.,  a  mixture  consisting  of  1  part  of  cement,  2  parts 


Fig.  56  Fig-  57 

of  sand,  and  4  parts  of  broken  stone  is  sometimes  used.  The 
New  York  building  laws  call  for  1  part  of  cement,  3  parts 
of  sand,  and  5  parts  of  broken  stone. 


ELEMENTS  OF  STONE  MASONRY 


47 


In  localities  where  stone  cannot  readily  be  obtained, 
broken  brick  or  terra  cotta  may  be  used  in  the  same  propor¬ 
tion  as  stone,  but  care  should  always  be  taken  to  use  good, 
hard-burned  material.  - 

Well-broken  foundry  slag  and  scoriae,,  clean  steam-boiler 
ashes  from  anthracite  coal,  and  clean-washed  gravel,  mixed 
in  the  proportions  given,  also  make  good  concrete. 

68.  Quicksand,  when  confined,  can  be  safely  built  on. 
Fig.  56  shows  a  method  of  confining  quicksand  by  sheet 
piling  and  placing  concrete  between  the  piling.  In  this  case, 
the  sheet  piling  showTn  at  a  is  placed  4  feet  apart.  The  con¬ 
crete,  shown  at  b,  is  2  feet  thick  and  extends  the  full  width 
of  the  piling.  The  quicksand,  through  which  the  sheet  piling 
is  driven,  is  shown  at  c,  and  the  20-inch  brick  foundation 
wall,  at  d. 

69.  Fig.  57  illustrates  a  footing  composed  partly  of 
timber.  The  footing  from  which  this  was  taken  was  placed 
near  the  water-line  of  a  marsh  in  New  York  state,  to  carry  a 
factory  building  50  ft.X80  ft.  and  40  feet  high.  The  soil 
was  a  stiff,  black  muck,  and  at  a  depth  of  about  5  feet,  water- 
soaked  sand  was  found.  After  the  trenches  were  dug,  a 
bedding  of  concrete  a  12  inches  thick  was  laid.  On  top  of 
this  concrete,  2-inch  spruce  planks  b  were  placed  crosswise, 
followed  by  8"X8"  timber  c,  laid  parallel,  with  the  trenches 
filled  in  between  with  concrete.  On  these  planks  and  concrete 
were  laid  the  base  stones  d,  and  on  top  of  these  stones  was 
built  a  20-inch  foundation  wall  e.  The  trenches  on  each  side 
of  the  wall  were  filled  in  with  sand,  rammed  down,  as  shown 
at  /. 

This  factory  building  contains  an  engine,  shafting,  boiler, 
and  machinery,  and,  besides,  over  one  hundred  employes  are 
constantly  at  work,  yet  no  settlement  has  occurred,  though 
it  has  been  built  a  number  of  years. 

70.  Stone-footing  courses  should  be  laid  with  large  flat 
stones  not  less  than  8  inches  thick.  If  more  than  one  course 
is  laid,  the  joints  should  never  come  over  each  other,  as  that 


48 


ELEMENTS  OF  STONE  MASONRY 


§32 


would  defeat  the  object  of  bonding,  which  is  to  tie  together 
firmly  the  parts  of  the  wall. 

All  stone  footings  should  lie  on  their  natural,  or  quarry, 
beds,  and  all  joints  and  spaces  between  the  stone  must  be 
well  filled  with  mortar.  The  mortar  acts  as  a  bedding 
between  the  stones,  and  unless  it  is  interposed,  the  uneven 
pressure  of  one  stone  on  another  might  cause  a  fracture  of 
one  and  produce  settlement. 

71.  All  footing  courses,  as  indeed  all  masonwork  below 
the  ground  level,  should  be  laid  in  cement  mortar.  The 
usual  proportion  of  cement  and  sand  for  cement  mortar  is 
1  part  of  cement  and  3  parts  of  sand.  The  proportions  just 
stated  are  from  the  building  laws  of  New  York,  and  have 
been  found  suitable  for  general  masonwork. 

72.  Stepped-up  brick  footings  having  concrete  and  stone 
bases,  as  shown  in  Figs.  51  and  52,  are  often  used.  The 
pyramidal  form  of  stepped-up  brickwork  carries  the  load  of 
the  superstructure  more  evenly  to  the  footings  and  reduces 
the  risk  of  settlement  or  fracture.  Nothing  except  good, 
hard,  well-burned  bricks  should  be  used,  and  these  should  be 
laid  in  cement  mortar,  and  should  break  joints — that  is,  no 
two  joints  should  come  over  each  other. 


SPECIAL  FOOTINGS 

73.  Footings  on  Rock  and  Gravel. — In  placing  foun¬ 
dation  footings  on  rock,  it  is  sometimes  found  that  some 
portions  of  the  footings  will  rest  on  the  rock,  and  others, 
owing  to  the  diversified  character  of  the  surface,  will  rest  on 
clay,  sand,  or  gravel.  The  settlement  of  the  foundation 
walls — and  as  a  necessary  consequence,  that  of  the  whole 
building — will  then  be  uneven,  as  the  walls  resting  on  the 
rock  will  not  settle,  while  those  resting  on  the  sand,  gravel,  or 
clay,  by  compressing  the  material  on  which  they  are  carried, 
will  settle. 


§32 


ELEMENTS  OF  STONE  MASONRY 


49 


74.  Fig.  58  illustrates  the  method  employed  to  obtain 
equal  settlement.  In  (a)  are  shown  the  rock  and  gravel  before 
leveling  or  excavating,  the  clay  or  sand  being  shown  at  a  and 
the  rock  at  b.  It  is  customary  to  remove  the  rock  to  a  certain 
level,  as  shown  in  ( b ).  The  softer  soil  a  is  then  removed 
and  leveled  off,  as  at  c  c,  and  a  bed  of  concrete  about  3  feet 
thick,  as  shown  at  d,  is  then  put  down.  This  concrete  is 
brought  to  the  level  of  the  rock,  as  at  b  b,  and  on  this  base  the 
brick  or  stone  foundation  wall  e  is  built. 

In  erecting  footings  on  solid  rock,  it  is  not  considered 
necessary  to  cut  the  footing  bed  level  over  the  entire  surface 


Fig.  58 


of  the  rock,  nor  even  to  cut  a  series  of  horizontal  surfaces 
resembling  steps,  as  is  frequently  done  in  softer  soils;  but  it  is 
necessary  to  roughen  the  surface  of  the  rock  so  as  to  prevent 
the  footing  from  slipping  on  its  foundation.  After  this  is 
done,  concrete  may  be  put  in  to  bring  the  foundation  to  its 
proper  level.  If  the  structure  is  to  be  only  three  or  four 
stories  in  height,  stone  or  brick  may  be  used  instead  of  con¬ 
crete,  but  a  concrete  base  is  usually  preferable. 

75.  Footing  on  Sloping  Ground. — Footing  courses 
built  on  slopes — especially  of  clay — are  always  liable  to 


50 


ELEMENTS  OF  STONE  MASONRY 


§32 


slide.  This  tendency  to  slide,  however,  may  be  overcome  by 
cutting  horizontal  steps  in  the  slope,  as  shown  in  Fig.  59, 
where  the  slope  e  f  is  stepped  off,  as  shown  at  a,  in  order  that 


Fig.  59 


the  footings  b  may  have  a  horizontal  bearing.  These  footings 
may  be  either  of  stone  or  of  concrete,  but  if  the  former 
material  is  used,  great  care  must  be  exercised  to  secure  a 
perfect  bond  at  the  stepping  places,  and  the  foundations 
should  be  laid  in  as  long  sections  as  possible. 

i 

76.  Inverted.  Arches. — When  a  wall  is  composed  of 
isolated  piers,  it  is  well  to  combine  all  their  footings  into  one, 
and  to  step  the  piers  down,  as  shown  in  Fig.  60.  In  this 


Fig.  60 


figure,  the  concrete  footing  course  is  shown  at  a;  the  stepped- 
up  foundations  of  the  piers,  at  6;  and  the  piers  resting  on  the 
footings,  at  c. 


ELEMENTS  OF  STONE  MASONRY 


51 


77.  If  there  is  not  sufficient  depth  to  step  the  founda¬ 
tions,  use  is  sometimes  made  of  inverted  arclies.  Such 
arches,  however,  are  to  be  avoided  unless  the  foundation  wall 
is  from  necessity  very  shallow,  as  great  care  is  required  to  lay 


them  properly,  and  the  slightest  settlement  in  the  arches  has  a 
disastrous  effect  on  the  piers. 


The  end  arch  of  the  building  must  have  a  pier  or  other 
support  of  sufficient  weight  or  strength  to  resist  the  thrust  of 
the  arch;  otherwise,  the  weight  might  throw  out  the  pier,  as 
shown  by  the  dotted  lines  at  a,  Fig.  61. 


52 


ELEMENTS  OF  STONE  MASONRY 


§32 


This  difficulty,  however,  can  be  overcome  by  using  an  iron 
rod,  with  iron  plates  and  nuts,  as  shown  in  Figs.  62  and  63, 
thus  securing  the  skewbacks  in  place. 

The  inverted  arches  turned  between  the  piers  should  be  at 
least  12  inches  thick,  or  should  extend  the  full  width  of  the 
piers.  They  should  also  rest  on  a  continuous  bed  of  con¬ 
crete  of  proper  area,  and  at  least  18  inches  in  thickness;  or, 
they  may  rest  on  two  footing  courses  of  large  stone,  the  bottom 
course  being  laid  as  stretchers  and  the  top  course  as  headers. 


Fig.  63 


78.  Fig.  62  illustrates  two  piers,  each  3  feet  square,  con¬ 
nected  by  a  brick-and-concrete  inverted  arch.  At  a  is  shown 
the  18  inches  of  concrete  under  the  12  inches  of  brickwork  b. 
At  c  and  c'  are  shown  the  stone  skewbacks  from  which  the 
brick  arches  spring,  and  at  d  is  shown  the  2-inch  iron  rod  that 
ties  the  end  pier  e'  to  the  second  pier  e ,  and  thus  prevents  the 
thrusting  out  of  the  end  pier. 

Fig.  63  shows  an  inverted  arch  built  of  stone,  24  inches 
thick.  At  a  is  shown  the  stone  arch  maintained  in  position 
by  the  iron  tie-rod  b ,  and  at  c  the  brick  foundation  piers  are 
shown  on  the  skewbacks  d. 


ELEMENTS  OF  STONE  MASONRY 


53 


stem 


M$0M 


U*  \lvAi  vj '.r‘>,?a.'i4  y/*vyv  wr  ?#.<*% 


79.  The  best  form  of  inverted  arch  is  the  three -centered, 
or  elliptic;  next,  the  pointed;  third,  the  circular;  and  lastly, 
the  segmental  arch. 

The  method  of  getting  the  lines  for  the  centering  in  an 
elliptic  arch  is  as  follows:  Divide  the  space  shown  on  the 
line  from  a  to  b,  Fig.  64,  into  three  equal  parts,  at  d,  d;  then 
draw  three  circles  with  centers  c,  so  that  the  circumferences 
of  these  circles  will  be  tangent  at  d.  From  the  center  of  the 
middle  circle  draw  the  perpendicular  c  ) ;  the  point  f  where  it 
intersects  the  circle  is  the  center  of  the  arch  from  g  to  h. 
F rom  f  draw  lines  /  g  and  /  h  of  indefinite  lengths  through 


points  d,  d.  With  a  d  as  the  radius,  draw  arc  a  g  intersecting 
line  f  g  at  g.  Then,  with  f  g  as  the  radius,  draw  the  arc  g  h; 
and  from  h,  arc  h  d  with  b  d  as  the  radius. 

At  k  is  shown  the  brick  arch,  which  is  12  inches  deep,  and 
at  l,  the  concrete  under  it.  This  form  of  arch  is  used  fre¬ 
quently  in  the  construction  of  sewers. 


Fig.  64 


54 


ELEMENTS  OF  STONE  MASONRY 


§32 


THICKNESS  OF  WALES 

80.  Foundation  Walls. — A  very  good  rule  to  fix  the 
thickness  of  rubble-stone  foundation  walls  is,  that  they  shall 
be  at  least  8  inches  thicker  than  the  wall  next  above  them,  for 
a  depth  of  12  feet  below  grade  or  curb  level;  and  they  should 
be  increased  4  inches  in  thickness  below  that  point,  for  every 
additional  10  feet  or  less  in  depth.  Thus,  if  the  first-story 
walls  are  12  inches  thick,  the  stone  foundation  walls  would 
have  to  be  20  inches  thick  for  12  feet  in  depth,  and  24  inches 
thick  below  that  point  for  10  feet  or  less.  Rubble-stone 
foundations  walls  are  seldom  made  less  than  18  inches  in 
thickness.  A  wall  18  inches  thick  is  not  always  needed  to 
carry  the  superimposed  weight,  but  smaller  walls  are  more 
expensive  to  build  and  consequently  are  seldom  constructed. 

The  thickness  of  foundation  walls  in  all  the  large  cities  is 
controlled  by  the  building  laws.  Where  there  are  no  existing 
laws,  Table  I  will  serve  as  a  guide. 


TABLE  I 

THICKNESS  OF  FOUNDATION  WALLS 


Height  of  Building 

Dwellings,  Hotels,  Etc. 

Warehouses 

Brick 

Inches 

Stone 

Inches 

Brick 

Inches 

Stone 

Inches 

Two  stories . 

12  to  1 6 

20 

16 

20 

Three  stories . 

16 

20 

20 

24 

Four  stories . 

20 

24 

24 

28 

Five  stories . 

24 

28 

24 

28 

Six  stories . 

24 

28 

28 

32 

81.  Stone  Walls. — The  laws  regarding  the  thickness 
of  stone  walls  differ  in  the  various  cities,  and  no  uniform 
rules  can  be  given,  ^or  ashlar  work,  the  New  York  law  states 
that,  “where  walls  or  piers  are  built  of  coursed  stones,  with 
dressed  level  beds  and  vertical  joints,  the  Department  of 


§32 


ELEMENTS  OF  STONE  MASONRY 


55 


Buildings  shall  have  the  right  to  allow  such  walls  or  piers  to 
be  built  of  a  less  thickness  than  specified  for  brickwork,  but 
in  no  case  shall  said  walls  or  piers  be  less  than  three-quarters 
of  the  thickness  provided  for  brickwork.” 

The  following  regulations  apply  to  the  District  of  Columbia 
for  rubblework:  “Walls  laid  with  rubble  work  shall  be  one- 
fourth  thicker  than  required  for  brick  walls,  but  never  less 
than  18  inches  thick;  they  must  be  constructed  with  flat 
stone,  sound  and  durable,  laid  on  their  natural  beds,  and 
brought  to  a  level  every  3  feet  in  height.  They  must  be 
built  between  two  lines,  shall  have  bond  stone  or  headers 
extending  through  the  thickness  of  the  walls  at  intervals  not 
exceeding  3  feet,  and  shall  be  laid  in  cement  mortar  composed 
of  2  parts  of  sand  and  1  part  of  cement.  No  rubble  wall 
shall  be  located  as  a  party  wall  unless  the  written  consent  of 
the  adjoining  owner  shall  first  be  filed  in  the  office  of  the 
Inspector  of  Buildings.  The  restriction  as  to  location  of 
the  party  wall  above  mentioned  shall  not  apply  to  stone 
foundation  walls  which  support  brick  walls.” 

For  ashlar  facing,  the  requirements  for  the  District  of 
Columbia  are  as  follows:  “Thin  ashlar  facing  shall  not  be 
counted  in  determining  the  thickness  of  walls.  If  stone 
facing  is  used  with  bond  courses  alternately,  not  less  than 
8  inches  thick,  on  the  beds,  then  such  facing  shall  be  counted  as 
forming  part  of  the  wall,  and  the  total  thickness  of  the  wall 
and  facing  shall  not  be  required  to  be  more  than  that  herein 
specified  for  walls  (meaning  brick)  but  never  less  than 
13  inches  thick.” 

The  thickness  of  brick  walls  will  be  considered  in  a  later 
Section. 

SIDEWALKS 

82.  Sidewalks  may  be  made  of  flagstones,  concrete,  or 
brick.  A  flag:  is  a  thin  slab  of  stone,  which  is  generally  used 
in  sidewalk  work.  Concrete  sidewalks  are  usually  finished 
on  top  with  cement  and  sand.  The  bricks  used  for  sidewalk 
work  should  be  hard  and  of  the  variety  known  as  paving 
brick. 


56 


ELEMENTS  OF  STONE  MASONRY 


§32 


83.  Stone  Sidewalks. — If  stone  of  a  texture  that 
readily  splits  into  flags  can  be  obtained,  it  will  probably 
make  a  better  and  cheaper  sidewalk  than  will  concrete.  A 


Fig.  65 

flag  sidewalk  can  be  taken  up  and  relaid  better  than  one  of 
concrete,  is  easier  to  repair,  and  is  also  more  durable. 


‘84.  The  stone  for  sidewalks  should  be  2  or  3  inches 
thick  when  used  in  areas  or  similar  places,  and  the  flags 
should  be  cut  rectangular.  They  should  be  laid  on  a  sand  or 
a  cinder  bed  that  is  2  or  3  inches  in  thickness.  The  edges  of 
the  stones  usually  rest  on  a  small  bed  of  concrete,  or  1-to-l 
cement  mortar  is  put  into  the  cracks  as  shown  at  c,  Fig.  65. 
In  this  way  is  obtained  a  joint  that  will  prevent  water  from 
soaking  down  between  the  flags  and  freezing.  In  countries 
where  there  is  no  frost,  this  concrete  and  cement  may  be 
omitted,  and  the  sidewalk  may  simply  be  laid  on  the  sand  bed. 


85.  Sidewalks  located  between  the  curb  and  the  building 
line  are  subjected  to  more  traffic  than  pavements  found  in 
areas,  etc.  and  should  therefore  be  built  in  a  more  substantial 


§32 


ELEMENTS  OF  STONE  MASONRY 


57 


manner.  The  flags  used  for  this  class  of  sidewalks  are  gener¬ 
ally  3  or  4  inches  thick.  It  is  always  best,  if  possible,  to 
have  the  stones  of  the  same  width  as  the  sidewalk,  but  for 
wide  sidewalks  this  is  impracticable.  When  there  is  danger 
of  frost  getting  under  the  sidewalk  and  thus  causing  it  to 
heave,  the  flags  should  be  supported  at  the  ends  only,  as 
shown  in  Fig.  6G.  A  12-inch  dwarf  wall  should  be  built 
at  the  curb  line,  as  shown  at  a,  and  carried  below  the  frost 
line.  The  curbstone  b  is  from  4  to  6  inches  thick,  and  is 
rabbeted  into  the  dwarf  wall.  At  c  is  shown  the  gutter,  and  d, 
the  stone  pavement,  which  is  supported  at  its  center  by  a 
dwarf  wall  e.  If  the  sidewalk  is  laid  in  two  courses,  or  if  it 
extends  to  the  building  line,  it  may  rest  on  a  break  in  the 
foundation  wall  /,  as  shown.  Under  the  sidewalk  at  g  is 
a  bed  of  sand  or  ashes. 

86.  Brick  Sidewalks. — In  constructing  brick  side¬ 
walks,  good,  hard  paving  bricks,  sound  and  square,  should  be 
used.  These  bricks  should  be  laid  flat,  herring-bone  fashion, 
on  a  bed  of  sand  that  is  from  4  to  6  inches  thick.  After  the 
bricks  are  laid  and  graded,  the  entire  surface  should  be  cov¬ 
ered  with  sand,  which  is  swept  over  the  bricks  until  the 
joints  are  thoroughly  filled.  If  extra  thickness  of  wearing 
surface  is  desired,  the  bricks  may  be  set  on  edge,  and  cov¬ 
ered  with  sand  as  described. 

87.  Cement  Sidewalks. — The  method  of  laying  cement 
sidewalks  is  as  follows:  The  ground  should  be  leveled  off 
from  12  to  15  inches  below  the  finished  grade  of  the  walk, 
and  should  be  well  settled  by  ramming,  care  being  taken 
that  the  excavation  is  drained  to  one  side.  A  foundation 
consisting  of  about  8  or  10  inches  of  coarse  gravel,  stone 
chips,  sand,  or  cinders,  should  then  be  laid  and  well  tamped 
or  rolled  with  a  heavy  roller.  An  attempt  often  is  made  to 
economize  on  this  kind  of  foundation  by  making  it  only 
5  or  6  inches  thick.  However,  foundations  of  such  thick¬ 
ness  generally  allow  the  frost  to  penetrate  to  the  ground 
and  heave  up  the  pavement  in  spots. 


58  ELEMENTS  OF  STONE  MASONRY  §  32 

After  the  foundation  has  been  rolled,  the  concrete  should 
be  prepared  in  the  proportion  of  1  part  of  cement,  3  parts  of 
sand,  5  parts  of  broken  stone,  and  a  sufficient  quantity  of 
water  to  make  a  stiff  mortar.  It  should  be  thoroughly  mixed 
and  worked  while  being  laid.  The  top,  or  finishing,  coat 
should  be  laid  immediately,  and  only  as  much  concrete 
should  be  laid  as  can  be  covered  with  cement  on  the  same 
day,  because  if  the  concrete  gets  dry  on  top,  the  finishing 
coat  will  not  adhere  to  it.  The  top  coat  should  be  prepared 
by  mixing  1  part  of  the  best  Portland  cement  with  2  parts 
of  fine  sand  or  2  parts  of  clean,  sharp,  crushed  granite  or  flint 
rock. 

A  ^-inch  space  should  be  left  between  the  curb  and  the 
pavement  and  between  the  building  line  and  the  pavement, 
to  allow  for  expansion  and  contraction.  This  space  should 
be  filled  with  cinders  or  ashes.  The  pavement  itself  should 
be  laid  off  into  blocks  6  feet  square  or  less.  These  blocks 
should  be  separated  from  one  another  by  sheets  of  tar  paper, 
which  should  extend  all  the  way  through  the  concrete.  It  is 
very  essential  that  grooves  be  made  with  a  trowel  in  the  top 
coat  directly  over  the  tar  paper,  so  that  if  the  concrete 
cracks  while  drying  out,  it  will  be  sure  to  part  in  these  grooves 
and  not  in  the  body  of  the  pavement. 

88.  Hair  cracks  are  often  caused  by  the  mortar  in  the 
top  coat  being  too  rich  in  cement.  If  the  pavement  is  trow¬ 
eled  too  much,  it  has  a  tendency  to  make  the  cement  float  to 
the  top;  this  is  as  liable  to  cause  hair  cracks  as  the  use  of 
too  much  cement.  If  the  top  coat  is  put  on  too  wet,  it  has 
the  same  effect. 

89.  In  many  cities,  the  law  requires  that  concrete  side¬ 
walks  be  finished  with  a  rough  surface.  Such  a  surface  is 
not  so  slippery  in  winter  as  a  smooth  finish;  it  also  possesses 
the  additional  advantages  that  it  is  easier  to  construct  and 
does  not  show  any  hair  cracks.  In  laying  such  a  surface,  the 
top  coat  is  leveled  with  a  straightedge  running  on  battens, 
one  set  on  each  side  of  the  walk.  The  battens  are  arranged 
so  that  the  part  of  the  walk  at  the  curb  will  be  lower  than  the 


§32 


ELEMENTS  OF  STONE  MASONRY 


59 


part  at  the  building  wall.  (This  pitch  is  controlled  by  city 
ordinances,  and  is  usually  4  inches  in  10  feet  for  all  sidewalks.) 
The  sidewalk  i&  then  left  until  it  has  almost  set,  before  it  is 
troweled.  It  should  be  troweled  as  little  as  possible,  and 
with  a  wooden  trowel  instead  of  one  made  of  steel.  After 
troweling,  it  should  be  covered  with  straw  and  kept  moist 
for  at  least  a  week.  The  less  the  sidewalk  is  smoothed  with 
the  straightedge  or  trowel,  and  the  more  it  is  rammed  instead, 
the  better  it  will  be. 


Fig.  67  shows  a  section  of  a  concrete  sidewalk,  the  ashes  or 
spalls  being  shown  at  a;  the  first  coat  of  concrete,  at  b\  the 
finishing  coat,  at  c\  the  street  paving,  at  d  \  and  the  joints  with 
tar  paper  in  them,  at  e. 


STRUCTURE  OF  BRICK 


MASONRY 

WALLS 


METHODS  OF  LAYING  BRICK 


DEFINITIONS 

1.  Bonding. — By  the  bonding  of  brickwork  is  meant 
the  process  of  laying  brick  across  one  another  so  that  one 
brick  will  rest  on  parts  of  two  or  three  bricks  below  it.  When 
built  in  this  manner,  it  is  difficult  for  a  wall  to  fail  by  simply 
parting  at  the  joints  without  breaking  the  brick. 

In  bricklaying,  all  corners  and  joints  should  be  carefully 
plumbed,  the  courses  of  brickwork  kept  perfectly  horizontal — 
which  necessitates  uniform  mortar  joints — and  the  wall 
surfaces,  both  exterior  and  interior,  kept  in  perfect  aline- 
ment.  All  these  conditions  may  have  been  complied  with, 
and  yet  the  work  may  be  imperfect;  the  merit  of  the  brick¬ 
work  must  be  judged  by  the  thoroughness  of  the  bond 
observed  in  every  portion  of  the  wall,  both  lengthwise  and 
crosswise.  This  bond  must  be  maintained  by  having  every 
course  perfectly  horizontal,  both  longitudinally  and  trans¬ 
versely,  as  well  as  perfectly  plumb.  Aside  from  the  quality 
and  character  of  the  material,  the  bonding  of  a  wall  con¬ 
tributes  most  to  its  strength. 

A  brick  is  designated  by  different  terms,  according  to  its 
position  in  the  wall.  When  placed  lengthwise  on  the  face 
of  the  wall,  as  at  a,  Fig.  1,  the  brick  is  termed  a  stretcher; 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS'  HALL.  LONDON 

§  33 


211—13 


i 


2 


ELEMENTS  OF  BRICK  MASONRY 


§33 


when  placed  crosswise  with  one  end  only  exposed  to  view, 
as  at  b,  it  is  called  a  header.  A  course  means  the  vertical 
thickness  of  a  brick  and  a  mortar  joint. 

2.  Keeping  the  Perpends. — To  obtain  the  best 
results  in  bonding  throughout  the  mass  of  the  wall,  strict 
attention  must  be  given  to  the  location  of  every  joint  in  the 
brickwork.  On  the  faces  of  the  wall,  the  vertical  joints  in 
each  course  throughout  the  height  should  be  kept  perpen¬ 
dicular,  or  directly  over  those  in  the  second  course  below. 
This  is  called  keeping  the  perpends.  The  joints 
across  the  top  of  the  wall  should  also  be  kept  in  line,  so  that 


Fig.  1 


if  the  perpends  are  observed  on  one  face  of  the  wall,  the 
other  face  will  also  work  up  correctly.  Even  when  the  wall 
is  exposed  on  only  one  face,  the  importance  of  having  the 
joints  on  top  of  the  wall  kept  in  line  is  just  as  essential; 
otherwise,  its  effective  longitudinal  bond  will  soon  be  lost, 
since  at  best  the  heading  bond  furnishes  a  lap  of  only 
2  inches. 

3.  Necessity  of  Preserving  Bonding. — The  impor¬ 
tance  of  having  the  bond  in  brickwork  preserved  in  the 
whole  wall  can  be  understood  by  referring  to  Fig.  1,  which, 
as  already  inferred,  shows  a  section  of  a  wall  consisting  of 


§33 


3 


ELEMENTS  OF  BRICK  MASONRY 


alternate  courses  of  stretchers  and  headers.  By  placing  the 
brick  as  shown,  no  longitudinal  bond  exists,  and  the  wall  is 
simply  a  series  of  contiguous  piers  that  join  one  another  at 
the  vertical  lines  c  d,  and  have  no  bond  or  union  between 
them  other  than  that  obtained  by  the  adhesion  of  the  mortar. 
This  is  because  none  of  the  brick  in  one  pier  overlaps  any 
brick  in  the  adjoining  piers.  This  method  manifestly  lacks 
strength  and  stability.  In  order,  therefore,  to  overcome 
this  constructive  difficulty  and  to  secure  a  continuous  bond 
in  the  length  of  the  wall,  recourse  is  had  to  a  different  arrange¬ 
ment  of  the  bricks  and  also  to  the  use  of  blocks  that  vary 
in  size  from  the  ordinary  brick. 


Fig.  2 


4.  Closers  and  Bats. — The  brick  of  different  sizes  used 
for  bonding  are  called  closers,  the  term  meaning  that 
they  perfectly  finish,  or  close,  the  length  of  the  courses  that 
have  been  adjusted  to  obtain  the  bond.  The  vertical  joint, 
which  is  shown  at  c  d,  Fig.  1,  is  avoided,  and  no  two  adjacent 
courses  have  joints  that  are  immediately  over  each  other. 
The  closers  are  made  by  cutting  the  brick  to  such  dimensions 
as  the  situation  requires,  the  operation  being  performed  by 
striking  a  brick  a  sharp  blow  with  the  edge  of  a  steel  trowel. 
The  cut  brick  are  called  bats,  and  are  designated  according 
to  the  proportion  that  each  bat  bears  to  the  whole  brick. 
Pressed  and  enameled  brick  are  often  cut  with  a  cold  chisel 
so  as  to  get  a  more  even  fracture. 


4 


ELEMENTS  OF  BRICK  MASONRY 


§33 


The  different  bats,  or  closers,  used  in  brickwork  are  shown 

in  Fig.  2,  (a)  representing  a  whole  brick  of  the  usual  size. 

If  a  brick  is  cut  longitudinally,  as  at  (6),  on  the  line  a  b, 

each  half  is  called  a  queen  closer;  but  as  it  is  difficult  to 

cut  the  full  length  in  this  manner,  the  usual  mode  is  first  to 

cut  the  brick  on  the  line  c  d  e,  and  then  cut  each  half  on  the 

# 

line  a  b.  If  the  brick  is  cut  as  at  (c),  it  is  called  a  king 
closer,  and  is  a  form  well  adapted  for  closers  at  door  and 
window  jambs.  If  one-fourth  of  the  whole  length  of  the 
brick  is  cut  off,  as  at  (d),  the  remainder  is  called  a  three- 
quarter  bat;  and,  in  a  like  manner,  the  portion  remaining 
at  ( e )  is  called  a  half  bat;  and  at  (/),  a  quarter  bat. 


BOND  IN  BRICKWORK 

5.  In  connection  with  the  use  of  closers,  whereby  the  lap 
is  properly  secured,  there  are  several  methods  of  placing  the 
brick  in  the  wall,  each  method  having  its  own  name  to 
indicate  the  kind  of  bond  used. 


6.  Heading  Bond. — When  all  the  courses  present  the 
end  of  the  brick  in  the  face  of  the  wall,  the  wall  is  then 


Fig.  3 

composed  entirely  of  headers ,  and  is  known  as  the  heading 
bond.  This  method  of  bonding,  however,  is  suitable  only 
for  sharp-curved  walls,  as  it  possesses  little  longitudinal  bond. 


§33 


ELEMENTS  OF  BRICK  MASONRY 


5 


7.  Stretching  Bond. — When  all  the  courses  consist  of 
stretchers,  the  stretching  bond  is  the  one  employed.  The 
wall  formed  by  this-  method  should  be  used  only  for  par¬ 
titions  that  are  not  greater  than  4  inches  in  thickness.  If  the 
wall  is  to  be  thicker,  the  method  should  not  be  followed,  as 
there  would  be  no  transverse  bond. 

8.  English  Bond. — In  the  English  bond,  the  header 
and  stretcher  courses  are  laid  alternately,  as  shown  in 
Fig.  3.  Joints  are  broken  in  the  longitudinal  bond  courses 
by  the  use  of  quarter-bat  closers,  as  shown  at  c.  The  joints 
can  also  be  broken  by  the  use  of  three-quarter  bats.  It 
will  be  observed  that  the  heart  of  the  wall  consists  entirely 


of  heading  bond,  and  that  the  joints  of  the  heading  course, 
as  at  a,  are  well  bonded  by  the  headers  of  the  stretching 
course,  as  at  b. 

9.  Flemish  Bond. — In  the  method  known  as  Flemish 
bond,  only  two-thirds  of  the  number  of  headers  that  occur 
in  English  bond  are  exposed,  and  each  course  is  composed 
of  a  header  and  a  stretcher  laid  alternately.  The  method  of 
laying  the  brick  in  Flemish  bond  is  shown  in  Fig.  4.  The 
lap  in  this  case  is  obtained  by  the  use  of  three-quarter  bats 
both  at  the  external  and  at  the  internal  angles  of  the  wall,  as 
shown  at  a  on  the  external  and  at  b  on  the  internal  angles. 
In  Flemish  bond,  the  closers  occur  in  the  heart  of  the  wall, 
just  as  was  shown  in  English  bond;  these  are  quarter,  half, 
and  three-quarter  bats,  as  shown  at  c. 


6 


ELEMENTS  OF  BRICK  MASONRY 


§33 


By  referring  to  the  illustration,  it  will  be  seen  that,  owing 
to  the  headers  and  stretchers  being  placed  on  the  inner  side 
of  the  wall  immediately  opposite  those  on  the  outer  face, 
both  faces  will  appear  exactly  alike  when  thus  arranged. 
The  wall  is  then  said  to  be  built  in  double  Flemish  bond. 

10.  Garden,  or  Running,  Bond. — The  bond  most 
extensively  used  in  the  United  States,  known  as  the  garden, 
or  running,  bond,  is  shown  in  Fig.  5.  This  bond,  which 
enables  the  bricklayer  to  build  a  larger  amount  of  wall  in  a 
given  time  than  does  either  the  English  or  the  Flemish 
bond,  is  sometimes  called  American  bond.  It  consists 
in  laying  from  four  to  seven  courses  as  stretchers  and  bond¬ 


ing  with  a  row  of  headers  at  regular  intervals.  The  longi¬ 
tudinal  lap  is  secured  by  closers,  as  shown  at  c.  The  heading 
course  in  the  heart  of  the  wall  is  shown  at  a,  being  placed 
immediately  over  the  heading  course  b  exposed  on  the  face. 

The  principal  defect  of  the  running  bond  is  that  the  wall, 
is  practically  composed  of  a  series  of  4-inch  layers  from 
12^  to  inches  in  height  that  have  no  transverse  bond  to 
the  adjoining  layers.  It  fulfils  the  requirements,  however,  if 
every  joint  throughout  the  body  of  the  wall  is  well  filled  with 
good  mortar  and  the  vertical  joints  are  well  rammed  with 
the  edge  of  the  trowel.  The  New  York  building  laws  require 
that  every  sixth  course  shall  be  a  header  course;  that  is, 
that  five  courses  of  stretchers  must  come  between  two  courses 


ELEMENTS  OF  BRICK  MASONRY 


7 


§33 

of  headers.  For  factory  and  warehouse  purposes,  where  the 
walls  have  to  sustain  heavy  weights,  it  is  better  to  have 
every  fourth  course  a  header  course,  thus  giving  three  courses 
of  stretchers  between  the  header  courses. 

The  wall  is  not  so  liable  to  split  in  its  thickness,  however, 
as  it  is  to  crack  longitudinally,  as  would  be  shown  by  a 
crack  up  and  down  the  face.  In  such  a  case,  the  garden 
bond  is  really  stronger  than  either  the  English  or  the  Flemish 


a 


n - 1 - r — 

rz  i  r  i 

_ 

rz 

ZZL 

L 

rz 

1  1  

1  1 

b  (a) 

a 

J 

L 

I 


b  (b) 


a 


J 

L 

nz  ~\ 

1 

I 

-  1  1 

i 

L 

rz 

-l_ i . . i 

_ 

b  (c) 


Fig.  6 

bond.  Of  course,  if  the  wall  cracks  exactly  vertically  the 
brick  will  be  broken  and  in  any  bond  the  same  number  of 
brick  will  crack.  Usually,  however,  a  crack  in  brickwork 
follows  the  mortar  joints,  as  shown  in  Fig.  6,  in  which  view 
(a)  represents  English  bond;  (6),  Flemish  bond;  and  (c),  gar¬ 
den  bond.  Nine  courses  of  brickwork  are  considered  in 
each  example,  and  in  each  case  the  probable  path  of  the 


8 


ELEMENTS  OF  BRICK  MASONRY 


§33 


crack  is  indicated  by  the  line  a  b.  As  can  be  seen  from  the 
illustration,  the  total  length  of  vertical  crack  in  each  case 
is  the  same.  However,  the  length  of  the  line  of  fracture,  or 
the  contact  area,  will  be  found  greater  in  the  garden  bond 
than  in  either  the  English  or  the  Flemish  bond,  because  the 
lap  of  the  brick  is  greater. 

11.  Bonding;  of  Face  Brick. — When  either  face  or 
pressed  brick  are  used  for  the  exterior  facing  of  a  wall,  it 
detracts  from  the  uniform  appearance  of  the  brickwork  if 
the  bonding  headers  appear  on  the  exterior  face  of  the  wall. 
This  difficulty  can  be  avoided  either  by  cutting  the  face 
brick  and  the  rough  brick  or  by  using  steel-wire  ties  to  bond 


the  brick  together.  If  no  tie  or  bond  is  used,  the  whole 
4  inches  of  brickwork  on  the  face  of  the  wall  will  have  no 
other  connections  with  the  rest  of  the  brick  than  that  given 
by  the  adhesion  of  the  mortar,  and  might  be  pushed  away 
bodily  from  the  rough  brick. 

12.  In  Fig.  7  is  shown  a  12-inch  wall  with  the  face  brick 
bonded  to  the  common  brick  by  what  is  known  as  diagonal, 
or  herring-bone,  bond.  At  a  is  shown  the  front  brick  cut 
at  the  angles;  at  b,  the  bonding  brick  laid  diagonally;  at  c, 
the  different-shaped  bats  laid  to  form  the  closers  of  the  bond 
brick;  and  at  d,  the  inside  course  of  stretchers.  It  is  cus¬ 
tomary  to  lay  an  inside  course  of  headers  immediately  over 
the  course  shown  in  the  figure. 


ELEMENTS  OF  BRICK  MASONRY 


9 


§33 

The  New  York  building  laws  require  that  “where  walls 
are  faced  with  brick  in  running  bond,  every  sixth  course 
shall  be  bonded  into  the  backing  by  cutting  the  corners  of 


Fig.  8 


the  face  brick  and  putting  in  diagonal  headers  behind,  or  by 
splitting  the  face  brick  in  half  and  backing  the  same  with  a 
continuous  row  of  headers.” 

The  second  method  just  mentioned  is  illustrated  in  Fig.  8. 
The  face  brick  cut  lengthwise  are  shown  at  a,  and  the  three- 
quarter  bats  bonding  in  back  of  the  face  brick  are  shown 
at  b.  The  whole  brick  c  bond  on  the  inside  of  the  wall,  and 
the  closer  d  closes  up  the  angle.  The  whole  face  brick  on 
the  corner  of  the  wall  is  shown  at  e. 


Fig.  9 


13.  In  Fig.  9  is  shown  one  method  of  bonding  face  brick 
with  metal  ties.  The  ties,  or  bonders,  b  are  made  either 
of  steel  or  of  galvanized-iron  wire  and  are  twisted  at  the 


ELEMENTS  OF  BRICK  MASONRY 


§33 


JO 

ends,  as  shown.  They  are  laid  in  every  sixth  course  of 
brick  and  are  placed  so  as  to  hold  together  the  outside 
course  a  and  the  inside  course  c.  The  principal  objection 
to  the  use  of  steel  or  iron  bonders  is  the  danger  of  rust, 
although  by  the  time  their  efficiency  has  been  destroyed  by 
the  action  of  rust,  the  mortar  used  should  have  hardened 
sufficiently  to  keep  the  face  brick  in  place. 

A  better  method  of  tying  front  brick  to  the  common  brick 
in  the  back  of  the  wall  is  to  use  perforated  steel  ties  that  are 
from  -3-2-  to  |  inch  thick  and  have  about  half  the  metal  punched 
out.  The  brick  may  be  brought  down  to  a  very  close  joint, 
and  the  clinching  spaces  make  a  very  firm  and  satisfactory 


Fig.  10 


binder.  Fig.  10  shows  the  application  of  these  bonding 
strips.  Here  the  pressed-brick  facing  is  shown  at  a,  the 
common  brick  in  the  back  of  the  wall  at  b,  and  the  perforated 
steel  ties  that  bond  the  pressed  brick  to  the  common  brick 
at  c. 

14.  Bonding  of  Hollow  Walls. — While  hollow  walls 
are  more  expensive  to  build  than  solid  walls,  they  are 
sometimes  used,  particularly  for  dwellings.  They  are  supe¬ 
rior  to  solid  walls  in  that  moisture  cannot  penetrate  them; 
also,  since  the  intervening  space  acts  as  an  insulating  medium, 
a  house  built  of  hollow  walls  is  cooler  in  summer  and  warmer 
in  winter  than  one  built  of  solid  walls. 


§33 


ELEMENTS  OF  BRICK  MASONRY 


11 


In  the  ideal  hollow  wall,  the  air  space  is  uninterrupted, 
having  no  braces  connecting  the  inner  and  outer  parts.  Of 
course,  in  practice,  it  is  necessary  to  have  some  bonding 


Fig.  11 


between  the  two  parts,  but  the  style  of  bonding  should  be 
carefully  considered.  By  permitting  the  passage  of  moisture 
through  the  wall  where  it  is  bonded,  brick  bonding  neutral¬ 
izes  some  of  the  benefit  derived  by  making  the  walls  hollow. 
To  provide  a  continuous  air  space  when  a  wall  is  penetrated 
by  openings  is  practically  impossible,  though  it  may  be 
closely  approximated. 

15.  Fig.  11  shows  one  form  of  hollow  wall  with  an  8-inch 
outer  wall  a,  a  2-inch  air  space  b,  and  a  4-inch  inner  wall  c. 
Except  at  the  corners,  this  wall  is  bonded  every  sixth  course 
in  height  and  every  12  inches  in  length,  as  shown  at  d.  The 
header  brick  e  that  join  the  bond  d  are  three-quarter  bats,  and 
the  bond  brick  have  a  bearing  of  2  inches  on  the  front  wall. 


Fig.  12  shows  a  10-inch  wall  that  has  a  4-inch  outer  wall  a, 
a  2-inch  air  space  b,  and  a  4-inch  inner  wall  c.  The  bond 
brick  are  cut  at  an  angle,  as  shown  at  d,  and  where  they  miter 


12 


ELEMENTS  OF  BRICK  MASONRY 


§33 


in  the  front  wall,  the  front  brick  are  also  cut,  as  at  e.  The 
2-inch  spaces  left  in  the  rear  wall  c  where  the  bond  brick 
occur  are  filled  with  quarter-bat  closers,  as  shown  at  /. 

16.  Probably  the  best  way  of  bonding  the  two  sides  of 
a  hollow  wall  is  to  use  metal  ties,  as  they  will  not  carry  any 
moisture  across,  especially  when  there  is  a  dip  or  sudden 
bend  in  their  length.  This  method  of  bonding  a  double 
wall  is  illustrated  in  Fig.  13.  At  a  is  shown  the  outer  4-inch 
wall;  at  b,  the  air  space;  at  c,  the  inner  4-inch  wall;  and  at  d, 
the  metal  ties.  These  ties  are  called  Morse  patent  ties. 

At  ( e ),  (/),  and  (g)  are  shown  other  forms  of  ties.  The 
form  shown  at  (g)  is  probably  the  best,  provided  the  walls 


Fig.  13 


are  more  than  one  brick  thick  so  that  the  turned-up  ends  of 
the  tie  will  not  show.  When  any  of  the  metal  ties  d,  ( e ),  or 
(/)  are  used,  they  should  be  spaced  every  24  inches  in  every 
fourth  course.  Since  the  form  of  tie  shown  at  (g)  is  stronger, 
it  need  be  used  only  in  every  eighth  course.  All  metal  ties 
should  be  dipped  in  hot  pitch  to  prevent  them  from  rusting. 

17.  Bonding  of  Walls  at  Angles.  —  In  building 
brick  walls,  it  is  necessary  that  the  angles  in  the  walls  be 
properly  bonded.  When  the  two  walls  forming  the  angle  are 
carried  up  at  the  same  time,  the  bonding  at  the  corners  is 
easily  effected;  if,  however,  one  wall  is  built  a  few  weeks 


§33 


ELEMENTS  OF  BRICK  MASONRY 


13 


ahead  of  the  other,  owing  to  a  delay  in  getting  materials 
required  for  it,  particular  care  must  be  taken  that  the  two 
parts  will  bond  together  properly. 

In  such  cases,  the  wall  first  built  is  generally  left  toothed, 
as  shown  in  Fig.  14.  In  order  to  unite  the  two  walls  more 
firmly,  anchors  made  of  f"  X  2" 
wrought  iron,  with  one  end  turned  up 
2  inches,  as  at  a,  and  the  other  bent 
around  a  f-inch  bar,  should  be  built 
into  the  side  wall  about  every  4  feet 
in  height,  as  shown  at  b.  These  an¬ 
chors  should  be  long  enough  to  extend 
at  least  12  inches,  or  the  depth  of  one 
and  one-half  brick  laid  the  long  way, 
into  the  side  wall,  and  the  center  of 
the  -f-inch  bar  should  be  about  8  inches 
from  the  back  of  the  front  wall. 

18.  In  regard  to  the  bonding  of 
angles,  the  New  York  building  laws 
are  as  follows: 

In  no  case  shall  any  wall  or  walls  of  any 
building  be  carried  up  more  than  two 
stories  in  advance  of  any  other  wall,  except 
by  permission  of  the  Com¬ 
missioner  of  Buildings 
having  jurisdiction,  but 
this  prohibition  shall  not 
include  the  enclosure  walls 
for  skeleton  buildings.  The 
front,  rear,  side,  and  party 
walls  shall  be  properly 
bonded  together,  or  an¬ 
chored  to  each  other  every  Fig.  14 

six  (6)  feet  in  their  height  by  wrought-iron  tie-anchors,  not  less  than 
one  and  one-half  (if)  inches  by  three-eighths  (§)  of  an  inch  in  size, 
and  not  less  than  twenty-four  (24)  inches  in  length.  The  side  anchors 
shall  be  built  into  the  side  or  party  walls  not  less  than  sixteen 
(16)  inches,  and  into  the  front  and  rear  walls,  so  as  to  secure  the 
front  and  rear  walls  to  the  side,  or  party,  walls  when  not  built  and 
bonded  together. 


14 


ELEMENTS  OF  BRICK  MASONRY 


§33 


DIFFICULTIES  IN  BRICKLAYING 

19.  Joining  New  Walls  to  Old  Walls. — In  join¬ 
ing  a  new  wall  to  one  that  has  been  built  for  some  time, 
especially  if  the  walls  come  at  right  angles,  the  new  work 
should  not  be  toothed,  or  bonded,  into  the  old  work  unless 
the  new  work  is  laid  up  in  cement  mortar.  All  masonwork 
built  with  lime  mortar  will  settle  somewhat,  owing  to  a  slight 
compresion  of  the  mortar  joints,  and  this  settlement  is  liable 
to  cause  a  crack  where  old  and  new  work  is  bonded  together. 
In  place  of  toothing,  if  lime  mortar  is  to  be  used,  a  groove 
usually  the  width  of  a  brick  should  be  cut  perpendicularly 
in  the  old  wall,  so  as  to  make  what  is'  known  as  a  slip  joint. 


Fig.  15  Fig.  16 


The  method  of  bonding  just  described  is  shown  in  Fig.  15. 
At  a  is  shown  the  groove,  or  chase,  cut  where  the  new  wall  is 
to  enter  in  the  old  wall,  while  at  c  is  shown  the  new  wall  and  d, 
the  old  wall. 

In  cheap  construction,  where  new  work  is  bonded  into 
old,  the  method  most  commonly  used  is  to  nail  a  piece  of 
2"  X  4"  timber  against  the  wall,  as  in  Fig.  16,  where  a  shows 
the  2"  X  4"  timber  spiked  to  the  old  wall  b  and  entering  the 
center  of  the  new  wall  c. 

20.  Laying  Brick  in  Severe  Weather. — When  brick 
are  dry,  they  absorb  moisture  from  the  mortar  in  which 
they  are  laid  and  thus  prevent  the  mortar  from  attaining  its 
customary  strength.  It  is  therefore  very  important,  espe¬ 
cially  in  warm  weather,  that  all  brick  be  wetted  with  water 
before  they  are  laid  in  the  wall. 


§33 


ELEMENTS  OF  BRICK  MASONRY 


15 


As  explained  in  Sands  and  Cements ,  neither  lime  nor  cement 
mortar  will  set  well  in  freezing  weather.  In  New  York 
City,  there  is  a  law  against  laying  brick  during  freezing 
temperatures,  but  the  law  is  not  enforced;  consequently,  in 
laying  brick,  it  seems  to  make  very  little  difference  to  the 
contractor  or  architect  whether  it  is  summer  or  winter — the 
work  goes  on  just  the  same.  On  account  of  this  disregard 
for  the  laws,  many  buildings  erected  during  freezing  weather 
either  collapse  or  become  weakened  as  soon  as  the  weather 
gets  warm.  On  the  first  warm  spring  day  in  1905,  in  New 
York  City,  six  large  buildings  of  the  “flat -house”  type  under 
construction  fell  in  for  no  other  reason  than  that  just  stated. 
These  buildings  would  probably  never  have  collapsed  had 
proper  precautions  been  taken. 


THICKNESS  OF  BRICK  WALES 

i 

21.  Size  of  Brick  and  Mortar  Joints. — There  is  no 
standard  size  of  brick  in  America.  The  dimensions  of 
brick  vary  with  the  locality  and  also  with  the  maker.  In  the 
New  England  States,  the  average  size  of  common  brick  is 
about  7f  in.  X  3|  in.  X  2J  in.;  and  New  York  and  New 
Jersey  brick  will  run  about  8  in.  X  4  in.  X  2^  in.  Walls 
laid  in  these  brick  will  run  normally  8,  12,  16,  and  20  inches 
in  thickness  for  1,  1^,  2,  and  2\  brick.  Most  of  the  western 
common  brick  measure  8?  in.  X  4J  in.  X  2^  in.,  and  the 
thickness  of  the  walls  measures  about  9,  13,  18,  and  22  inches 
for  1,  1^,  2,  and  2\  brick.  On  the  seacoast  of  some  of  the 
Southern  States,  the  brick  are  made  with  a  large  percentage 
of  sand,  and  will  average  9  in.  X  4J  in.  X  3  in. 

Most  manufacturers  of  pressed  brick  use  molds  of  the 
same  size;  hence,  pressed  brick  are  more  uniform  in  size. 
They  are  generally  8f  in.  X  4J  in.  X  2f  in.  Pressed  brick 
are  also  made  1?  inches  thick.  A  form  frequently  used  and 
known  as  Roman,  or  Pompeian,  brick  is  12  in.  X  4  in.  X  1  \  in. 
in  size.  In  order  that  a  good  bond  may  be  secured,  brick 
should  be  made  of  such  size  that  two  headers  and  a  joint 
will  equal  one  stretcher. 


16 


ELEMENTS  OF  BRICK  MASONRY 


§33 


In  ordinary  brickwork,  the  joints  should  not  average  more 
than  i  inch  in  thickness.  In  pressed  brickwork,  however,  the 
joints  may  be  made  smaller,  probably  J  to  A  inch,  because 
the  brick  are  smoother  and  have  no  irregular  projections. 

22.  Laws  Governing  Thickness  of  Walls. — In  order 
that  the  design  and  construction  of  walls  for  buildings 
of  various  dimensions  used  for  dwellings,  warehouses,  and 
other  purposes  may  be  carried  out  intelligently,  a  knowledge 
of  the  thickness  of  walls  required  is  very  important.  With 
this  object  in  mind,  an  extract  is  given  from  the  building 
laws  of  New  York  City  that  relate  to  the  thickness  of  brick 
walls  in  proportion  to  their  height.  The  laws  of  other  cities 
do  not  differ  very  materially  from  the  New  York  laws,  and 
these  may  therefore  be  safely  taken  as  a  standard. 


WALLS  FOR  DWELLING  HOUSES 

The  expression  “walls  for  dwelling  houses”  shall  be  taken  to  mean 
and  include  in  this  class  walls  for  the  following  buildings:  Dwellings, 
asylums,  apartment  houses,  convents,  club  houses,  dormitories,  hos¬ 
pitals,  hotels,  lodging  houses,  tenements,  parish  buildings,  schools, 
laboratories,  studios. 

1.  The  walls  above  the  basement  of  dwelling  houses  not  over  three 
stories  and  basement  in  height,  nor  more  than  40  feet  in  height,  and 
not  over  20  feet  in  width,  and  not  over  55  feet  in  depth,  shall  have 
side  and  party  walls  not  less  than  8  inches  thick  [see  Fig.  17  (a)],  and 
front  and  rear  walls  not  less  than  12  inches  thick. 

2.  All  walls  of  dwellings  exceeding  20  feet  in  width  and  not 
exceeding  40  feet  in  height,  shall  be  not  less  than  12  inches  thick  [see 
Fig.  17  (6)]. 

3.  All  walls  of  dwellings  26  feet  or  less  in  width  between  bearing 
walls  which  are  hereafter  erected  or  which  may  be  altered  to  be  used 
for  dwellings  and  being  over  40  feet  in  height  and  not  over  50  feet  in 
height,  shall  be  not  less  than  12  inches  thick  above  the  foundation 
walls  [see  Fig.  17  (c)]. 

No  wall  shall  be  built  having  a  12-inch-thick  portion  measuring 
vertically  more  than  50  feet. 

4.  If  over  50  feet  in  height  and  not  over  60  feet  in  height,  the  walls 
shall  be  not  less  than  16  inches  thick  in  the  story  next  above  the  foun¬ 
dation  walls  and  from  thence  not  less  than  12  inches  to  the  top  [see 
Fig.  i7  m 


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§  33 


ELEMENTS  OF  BRICK  MASONRY 


19 


5.  If  over  60  feet  in  height,  and  not  over  75  feet  in  height, 
the  walls  shall  be  not  less  than  16  inches  thick  above  the  foundation 
walls  to  the  height  of  25  feet,  or  to  the  nearest  tier  of  beams  to  that 
height,  and  from  thence  not  less  than  12  inches  thick  to  the  top  [see 
Fig.  17  (*?)]. 

6.  If  over  75  feet  in  height,  and  not  over  100  feet  in  height,  the 
walls  shall  be  not  less  than  20  inches  thick  above  the  foundation  walls 
to  the  height  of  40  feet  or  to  the  nearest  tier  of  beams  to  that  height, 
thence  not  less  than  16  inches  thick  to  the  height  of  75  feet,  or  to  the 
nearest  tier  of  beams  to  that  height,  and  thence  not  less  than  12  inches 
thick  to  the  top  [see  Fig.  17  (/)]. 

7.  If  over  100  feet  in  height,  and  not  over  125  feet  in  height,  the 
walls  shall  be  not  less  than  24  inches  thick  above  the  foundation  walls 
to  the  height  of  40  feet,  or  to  the  nearest  tier  of  beams  to  that  height; 
thence  not  less  than  20  inches  thick  to  the  height  of  75  feet,  or  to  the 
nearest  tier  of  beams  to  that  height;  thence  not  less  than  16  inches 
thick  to  the  height  of  110  feet,  or  to  the  nearest  tier  of  beams  to 
that  height;  and  thence  not  less  than  12  inches  thick  to  the  top  [see 
Fig.  17  (*)]. 

8.  If  over  125  feet  in  height  and  not  over  150  feet  in  height,  the 
walls  shall  be  not  less  than  28  inches  thick  above  the  foundation  walls 
to  the  height  of  30  feet,  or  to  the  nearest  tier  of  beams  to  that  height; 
thence  not  less  than  24  inches  thick  to  the  height  of  65  feet,  or  to  the 
nearest  tier  of  beams  to  that  height;  thence  not  less  than  20  inches 
thick  to  the  height  of  100  feet,  or  to  the  nearest  tier  of  beams  to  that 
height;  thence  not  less  than  16  inches  thick  to  the  height  of  135  feet, 
or  to  the  nearest  tier  of  beams  to  that  height ;  and  thence  not  less  than 
12  inches  thick  to  the  top  [see  Fig.  17  (h)]. 

9.  If  over  150  feet  in  height,  each  additional  30  feet  in  height  or 
part  thereof,  next  above  the  foundation  walls,  shall  be  increased 
4  inches  in  thickness,  the  upper  150  feet  of  wall  remaining  the  same  as 
specified  for  a  wall  of  that  height. 

WALLS  FOR  WAREHOUSES 

The  expression  “walls  for  warehouses”  shall  be  taken  to  mean  and 
include  in  this  class  walls  for  the  following  buildings:  Warehouses, 
stores,  factories,  mills,  printing  houses,  pumping  stations,  refrigerating 
houses,  slaughter  houses,  wheelwright  shops,  cooperage  shops,  brew¬ 
eries,  light  and  power  houses,  sugar  refineries,  office  buildings,  stables, 
markets,  railroad  buildings,  jails,  police  stations,  court  houses,  observ¬ 
atories,  foundries,  machine  shops,  public  assembly  buildings,  armories, 
churches,  theaters,  libraries,  museums. 

1.  The  walls  for  all  warehouses,  25  feet  or  less  in  width  between 
walls  or  bearings,  shall  be  not  less  than  12  inches  thick  to  the  height 
of  40  feet  above  the  foundation  walls  [see  Fig.  18  (a)]. 


20 


ELEMENTvS  OF  BRICK  MASONRY 


§33 


2.  If  over  40  feet  in  height,  and  not  over  60  feet  in  height,  the 
walls  shall  be  not  less  than  16  inches  thick  above  the  foundation  walls 
to  the  height  of  40  feet,  or  to  the  nearest  tier  of  beams  to  that  height, 
and  thence  not  less  than  12.  inches  thick  to  the  top  [see  Fig.  18  (6)]. 

3.  If  over  60  feet  in  height,  and  not  over  75  feet  in  height,  the 
walls  shall  be  not  less  than  20  inches  thick  above  the  foundation  walls 
to  the  height  of  25  feet,  or  to  the  nearest  tier  of  beams  to  that  height, 
and  thence  not  less  than  16  inches  thick  to  the  top  [see  Fig.  18  (c)]. 

4.  If  over  75  feet  in  height,  and  not  over  100  feet  in  height,  the 
walls  shall  be  not  less  than  24  inches  thick  above  the  foundation  walls 
to  the  height  of  40  feet,  or  to  the  nearest  tier  of  beams  to  that  height; 
thence  not  less  than  20  inches  thick  to  the  height  of  75  feet,  or  to  the 
nearest  tier  of  beams  to  that  height;  and  thence  not  less  than  16  inches 
thick  to  the  top  [see  Fig.  18  (d)]. 

5.  If  over  100  feet  in  height,  and  not  over  125  feet  in  height,  the 
walls  shall  be  not  less  than  28  inches  thick  above  the  foundation  walls 
to  the  height  of  40  feet,  or  to  the  nearest  tier  of  beams  to  that  height; 
thence  not  less  than  24  inches  thick  to  the  height  of  75  feet,  or  to  the 
nearest  tier  of  beams  to  that  height;  thence  not  less  than  20  inches 
thick  to  the  height  of  110  feet,  or  to  the  nearest  tier  of  beams  to  that 
height;  and  thence  not  less  than  16  inches  thick  to  the  top  [see 
Fig.  18  (e)]. 

6.  If  over  125  feet  in  height,  and  not  over  150  feet,  the  walls  shall 
be  not  less  than  32  inches  thick  above  the  foundation  walls  to  the 
height  of  30  feet,  or  to  the  nearest  tier  of  beams  to  that  height;  thence 
not  less  than  28  inches  thick  to  the  height  of  65  feet,  or  to  the  nearest 
tier  of  beams  to  that  height ;  thence  not  less  than  24  inches  thick  to  the 
height  of  100  feet,  or  to  the  nearest  tier  of  beams  to  that  height;  thence 
not  less  than  20  inches  thick  to  the  height  of  135  feet  or  to  the  nearest 
tier  of  beams  to  that  height;  and  thence  not  less  than  16  inches  to  the 
top  [see  Fig.  18  (/)]. 

7.  If  over  150  feet  in  height,  each  additional  25  feet  in  height,  or 
part  thereof  next  above  the  foundation  walls  shall  be  increased  4  inches 
in  thickness,  the  upper  150  feet  of  wall  remaining  the  same  as  specified 
for  a  wall  of  that  height. 

23.  Thickness  of  Walls  in  Different  Cities. 

Although  alike  in  the  main,  the  building  laws  of  the  several 
cities  differ  from  one  another  in  many  points,  particularly 
in  the  methods  of  measuring  the  thickness  of  walls.  For 
this  reason,  Tables  I,  II,  and  III  have  been  compiled,  the 
first  two  giving  the  thickness  of  warehouse  walls  and  the 
third  the  thickness  of  walls  for  residences.  Some  cities,  as, 
for  instance,  New  York  and  Boston,  give  the  height  of  walls 


§33 


ELEMENTS  OF  BRICK  MASONRY 


21 


in  feet;  others,  notably  New  Orleans  and  Denver,  measure 
the  heights  in  stories;  while  still  others,  as  Washington  and 
Cleveland,  specify  that  a  certain  thickness  of  wall  shall 
extend  to  a  certain  story,  but  state  that  this  story  must  not 
be  more  than  a  given  number  of  feet  from  the  foundation. 
Therefore,  in  preparing  the  tables,  several  heights  of  stories 
were  selected,  so  that  all  the  laws  could  be  made  to  apply  to 
the  same  case.  In  every  instance  where  the  law  required 
that  the  walls  be  thicker  as  the  building  is  made  wider,  the 
minimum  width  was  used;  as  in  New  York,  25-foot  span  for 
warehouses,  and  in  Philadelphia,  26-foot  span.  It  will  be 
noticed  in  Tables  I  and  II  that  dimensions  for  very  high 
buildings  are  not  given  for  some  cities.  This  is  because 
the  height  of  buildings  in  many  cases  is  limited  in  those 
localities.  In  Denver,  a  building  cannot  be  over  125  feet  in 
height,  and  in  Washington,  the  government  has  limited  the 
height  to  130  feet. 

The  thickness  of  the  walls  in  nearly  all  the  cities  is  given 
in  inches.  In  Cleveland,  however,  the  law  gives  the  thick¬ 
ness  of  the  wall  in  the  number  of  brick,  but  the  size  of  the 
brick  and  the  thickness  of  the  mortar  joints  are  also  speci¬ 
fied,  so  that  the  figures  can  easily  be  reduced  to  inches.  In 
Washington,  the  thickness  of  walls  of  residences  is  specified, 
and  a  note  states  that  4^  inches  must  be  added  to  this  thick¬ 
ness  for  warehouse  walls.  In  Tables  I  and  II,  however, 
5  inches  instead  of  4^  inches  is  added,  so  as  to  eliminate  all 
fractions.  It  will  be  noted  that  some  laws  call  a  wall  that  is 
evidently  a  brick  and  one-half  thick  12  inches,  while  others 
call  it  13  inches.  This  is  due  to  different  customs  in  different 
cities  and  the  different  sizes  of  brick  used.  As  the  laws  gov¬ 
erning  the  thickness  of  foundations  differ  greatly  according  to 
the  locality,  they  cannot  be  given  here ;  however,  they  may  be 
found  in  the  ordinances  of  the  city  or  town  in  which  the  build¬ 
ing  is  to  be  erected  and  are  usually  from  4  to  8  inches  thicker 
than  the  wall  directly  above  them.  In  some  of  the  cities,  as, 
for  instance,  Philadelphia,  Boston,  and  New  Orleans,  walls  of 
the  same  thickness  are  used  for  both  warehouses  and  residences 
Tables  I,  II,  and  III  apply  to  brick  walls  only. 


TABILE  I 

THICKNESS  OF  BRICK  WALES  FOR  WAREHOUSES  UP  TO 

SEVEN  STORIES  IN  HEIGHT 


Name  of  City 

Number  of  Stories 
and  Height  of 
Building 

Story  and  Height  of  Each 

First 

19' 

Second 
13'  4" 

Third 

13'  4" 

Fourth 
13'  4" 

Fifth 

13'  4" 

Sixth 
13'  4" 

Seventh 
i3'  4" 

Thickness  of  Brick  Wall,  in  Inches 

Washington  . . . 

14 

14 

St.  Louis . 

18 

13 

Denver . 

13 

13 

Memphis . 

13 

13 

Boston . 

16 

12 

New  York . 

Two  stories 

12 

12 

Philadelphia. .  . 

32  feet  4  inches 

l8 

13 

Chicago . 

12 

12 

Minneapolis  . .  . 

12 

12 

New  Orleans. . . 

13 

13 

Cleveland . 

13 

13 

San  Francisco  . 

17 

13 

Washington  . . . 

2  3 

18 

18 

St.  Louis . 

18 

18 

13 

Denver . 

17 

17 

13 

Memphis . 

i7 

1 7 

13 

Boston . 

20 

16 

16 

New  York . 

Three  stories 

16 

16 

12 

Philadelphia.  .  . 

45  feet  8  inches 

22 

13 

13 

Chicago . 

16 

12 

12 

Minneapolis  .  .  . 

16 

12 

12 

New  Orleans . . . 

13 

r3 

13 

Cleveland . 

17 

13 

13 

San  Francisco  . 

17 

17 

13 

Washington  . . . 

23 

18 

18 

18 

St.  Louis . 

22 

18 

18 

13 

Denver . 

21 

17 

17 

13 

Memphis . 

21 

17 

17 

13 

Boston . 

20 

16 

16 

16 

New  York . 

Four  stories 

16 

16 

16 

12 

Philadelphia. .  . 

59  feet 

22 

18 

13 

13 

Chicago . 

20 

16 

16 

12 

Minneapolis  . .  . 

16 

16 

12 

12 

New  Orleans. . . 

18 

18 

13 

13 

Cleveland . 

17 

r7 

13 

J3 

San  Francisco  . 

17 

17 

17 

13 

22 


TABLE  I — ( Continued ) 


Name  of  City 

• 

Number  of  Stories 
and  Height  of 
Building 

Story  and  Height  of  Each 

First 

19' 

Second 
13'  4" 

Third 

13'  4" 

Fourth 
13'  4" 

Fifth 

13'  4" 

Sixth 
13'  4" 

Seventh 
13'  4" 

Thickness  of  Brick  Wall,  in  Inches 

Washington  . . . 

27 

23 

23 

23 

18 

St.  Louis . 

22 

22 

18 

18 

13 

Denver . 

21 

21 

17 

17 

13 

Memphis . 

21 

21 

17 

x7 

17 

Boston . 

20 

20 

20 

20 

16 

New  York . 

Five  stories 

20 

l6 

16 

16 

16 

Philadelphia. .  . 

72  feet  4  inches 

26 

l8 

18 

13 

13 

Ch  icago . 

20 

20 

16 

16 

16 

Minneapolis  . .  . 

20 

l6 

16 

12 

12 

New  Orleans. . . 

l8 

l8 

18 

13 

13 

Cleveland . 

17 

17 

17 

1 t 

•  it 

San  Francisco  . 

21 

17 

17 

17 

13 

» 

Washington  . . . 

31 

27 

23 

23 

23 

18 

St.  Louis . 

26 

22 

22 

18 

18 

13 

Denver . . 

26 

21 

21 

17 

17 

13 

Memphis . 

25 

21 

21 

17 

17 

17 

Boston . j  .  . 

24 

20 

20 

20 

20 

16 

New  York . 

Six  stories 

24 

24 

24 

20 

20 

16 

Philadelphia.  .  . 

85  feet  8  inches 

26 

22 

l8 

l8 

13 

13 

Chicago ....... 

20 

20 

20 

l6 

16 

16 

Minneapolis  . .  . 

20 

20 

l6 

l6 

16 

12 

New  Orleans. . . 

22 

18 

l8 

l8 

13 

13 

Cleveland . 

22 

17 

17 

17 

13 

13 

San  Francisco  . 

21 

21 

17 

17 

17 

13 

Washington  . . . 

31 

27 

27 

23 

23 

23 

18 

St.  Louis . 

26 

26 

22 

22 

18 

l8 

x3 

Denver . ,  .  . 

26 

21 

21 

21 

17 

17 

17 

Memphis .  .  .  ,  .  . 

25 

21 

21 

21 

17 

17 

i7 

Boston . 

24 

20 

20 

20 

20 

20 

16 

Seven  stories 

New  York . 

24 

24 

24 

20 

20 

l6 

16 

Philadelphia. .  . 

yy  ICCi 

3° 

22 

22 

l8 

18 

13 

x3 

Chicago ....... 

20 

20 

20 

20 

16 

l6 

16 

Minneapolis  . .  . 

'  20 

20 

20 

l6 

16 

l6 

12 

New  Orleans. . . 

22 

22 

l8 

l8 

18 

13 

*3 

Cleveland . 

22 

22 

17 

17 

17 

x3 

13 

23 


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26 


TABTjE  III 

THICKNESS  OF  BRICK  WALLS  FOR  DWELLING  HOUSES 


Name  of  City 

Number  of  Stories 
and  Height  of 
Building 

First 

12' 

Second 

11' 

Third 
10'  6" 

Fourth 

10' 

Fifth 

10'  1 

Sixth 

10' 

Seventh 

10' 

Eighth 

io' 

Thickness  of  Brick  Wall 

in  Inches 

New  York  . 

12 

12 

Denver  .... 

13 

13 

W  ashington 

Two  stories 

9 

9 

Cleveland .  . 

23  feet 

13 

x3 

Chicago.  .  .  . 

12 

8 

Memphis. . . 

13 

13 

New  York  . 

12 

12 

12 

Denver  .... 

17 

13 

I3 

Washington 

Three  stories 

9 

9 

9 

Cleveland .  . 

33  feet  6  inches 

13 

13 

13 

Chicago. .  .  . 

12 

12 

8 

Memphis. . . 

13 

13 

13 

New  York  . 

12 

12 

12 

12 

Denver  .... 

17 

17 

13 

13 

Washington 

Four  stories 

13 

13 

13 

13 

Cleveland .  . 

43  feet  6  inches 

18 

13 

13 

13 

Chicago.  . .  . 

16 

16 

12 

12 

Memphis. . . 

13 

13 

13 

13 

New  York  . 

16 

12 

12 

12 

12 

Denver  .... 

21 

21 

17 

17 

13 

Washington 

Five  stories 

18 

13 

13 

13 

13 

Cleveland .  . 

53  feet  6  inches 

18 

18 

13 

13 

13 

Chicago. .  .  . 

16 

16 

16 

12 

12 

Memphis .  .  . 

17 

13 

13 

13 

13 

New  York  . 

16 

16 

12 

*  12 

12 

12 

Denver  .... 

26 

21 

21 

17 

17 

13 

Washington 

Six  stories 

22 

18 

18 

13 

13 

13 

Cleveland .  . 

63,  feet  6  inches 

18 

18 

18 

13 

13 

13 

Chicago.  . .  . 

20 

16 

16 

16 

12 

12 

Memphis.  .  . 

17 

17 

13 

13 

13 

13 

New  York  . 

16 

16 

12 

12 

12 

12 

12 

Denver  .... 

26 

21 

21 

21 

17 

17 

17 

Washington 

Seven  stories 

22 

18 

18 

18 

13 

13 

!3 

Cleveland .  . 

73  feet  6  inches 

18 

18 

18 

18 

13 

13 

13 

Chicago. . .  . 

24 

20 

20 

16 

16 

12 

12 

Memphis. .  . 

17 

r7 

I7 

13 

13 

13 

13 

New  York  . 

20 

20 

20 

16 

16 

l6 

l6 

12 

Denver  .... 

3° 

26 

21 

21 

21 

17 

17 

l7 

Washington 

Eight  stories 

26 

22 

18 

18 

18 

13 

13 

13 

Cleveland .  . 

83  feet  6  inches 

22 

18 

18 

18 

18 

13 

!3 

L3 

Chicago.  . . . 

24 

24 

20 

20 

16 

l6 

12 

12 

Memphis. . . 

21 

J7 

!7 

l7 

13 

13 

13 

!3 

27 


28 


ELEMENTS  OF  BRICK  MASONRY 


§33 


TYPES  OF  BRICK  WALES 

24.  Solid  Walls. — The  solid  brick  walls  of  a  building  are 
not  waterproof.  A  driving  rainstorm  of  several  days’  dura¬ 
tion  will  sometimes  penetrate  even  a  2-foot  wall  and  by 
wetting  the  inside  surfaces,  spoil  whatever  interior  coverings 
the  wall  may  have. 

A  house  built  of  solid  walls  is  likely  to  be  cold  in  winter, 
warm  in  summer,  and  damp  at  all  times.  In  solid  brick¬ 
work,  there  is  always  a  lack  of  insulation  against  heat  and 
moisture. 

Air  is  about  the  best,  and  certainly  the  cheapest,  form  of 
insulation.  To  obtain  air  insulation,  several  methods  are 
resorted  to.  The  one  most  in  use  consists  in  furring  the 
inner  surface  of  outside  brick  walls  with  furring  strips  and 
then  fastening  lath  and  plaster  to  these  strips.  The  danger 
of  fire  spreading  from  floor  to  floor  through  the  spaces  between 
the  furring  strips,  especially  in  hospitals,  schoolhouses,  and 
isolated  private  residences,  has  caused  many  excellent 
authorities  to  recommend  the  use  of  hollow  brick  walls  in 
their  stead. 

25.  Hollow  Walls. — Hollow  walls  are  intended  to  keep, 
moisture  from  passing  through,  and,  by  providing  an  air 
space,  keep  the  building  much  cooler  in  summer  and  warmer 
in  winter.  Constructive  difficulties,  however,  largely  offset 
their  advantages,  so  that  hollow  walls  are  not  often  used  in 
the  United  States.  There  is  no  doubt  but  that  their  use  might 
be  much  extended  with  good  results,  more  especially  for 
isolated  buildings.  The  objections  to  hollow  walls  are  that 
more  ground  area  is  required  and  the  cost  of  construction 
is  greater. 

26.  Party  AYalls. — A  party  wall  is  a  wall  that  separates 
two  adjoining  buildings  and  carries  the  floor  and  roof  beams 
of  both  of  them.  A  party  wall  is  sometimes  owned  jointly 
by  the  two  persons  that  own  adjacent  property.  In  such 
cases  the  center  line  of  the  party  wall  marks  one  of  the 
boundary  lines  of  the  lot.  The  owner  of  one  of  two  adjoining 


§33 


ELEMENTS  OF  BRICK  MASONRY 


29 


lots  has  the  right  in  most  localities  to  build  a  party  wall  half 
way  on  the  property  on  either  side  of  the  dividing  line.  In 
this  case,  the  right  to  use  the  wall  for  floor  and  roof  beams 
for  another  building  may  be  purchased  from  the  owner. 

The  floor  loads  on  party  walls  are  twice  as  great  as  the 
load  on  an  outside  wall ;  besides  this,  the  necessity  for  thorough 
and  complete  fire  protection  is  greater  in  party  walls  than  in 
outside  walls,  because  those  on  the  outside  can  easily  be 
reached  in  case  of  fire,  while  party  walls,  being  enclosed  by 
other  walls,  are  more  difficult  of  access.  As  building  regu¬ 
lations  differ  materially  in  regard  to  the  thickness  of  party 
walls,  the  best  guide  for  determining  their  thickness  is  to 
make  them  4  inches  thicker  in  each  story  than  the  outside 
wall. 

27.  Curtain  Walls. — In  modern  skeleton  construction, 
the  floor  loads  in  a  building  are  carried  by  the  steel  frame, 
and  the  walls  called  curtain  walls  carry  no  load  other  than 
their  own  weight.  There  are  a  few  high  buildings  in  which 
the  walls  extend  down  to  the  foundations,  but  because  it  is 
desired  to  make  these  walls  thin  on  account  of  the  space  they 
occupy  and  the  high  price  of  real  estate  in  the  business 
sections  of  cities,  curtain  walls  are  generally  supported  on  the 
steel  frame  of  the  building,  usually  at  every  floor.  In  this 
way  much  thinner  walls  can  be  used,  and  valuable  space  can 
be  saved. 

28.  Some  authorities  call  walls  placed  in  between  col¬ 
umns  but  resting  on  their  own  foundation  and  not  supported 
by  .girders  curtain  walls ,  and  walls  supported  at  every  story 
or  every  other  story  by  girders,  enclosure  walls;  however, 
most  engineers  class  both  styles  as  curtain  ivalls.  Walls 
resting  entirely  on  their  foundations  and  not  supported  by 
girders  are  not  used  much  at  present.  If  they  are  used, 
they  should  not  be  allowed  to  touch  the  metal  columns,  as 
their  faster  rate  of  settlement  will  be  sure  to  cause  unsightly 
cracks. 

29.  Following  is  an  extract  in  regard  to  enclosure  walls 
from  the  New  York  City  building  laws: 


30 


ELEMENTS  OF  BRICK  MASONRY 


§33 


Walls  of  brick  built  in  between  iron  or  steel  columns,  and  supported 
wholly  or  in  part  on  iron  or  steel  girders,  shall  be  not  less  than  12  inches 
thick  for  75  feet  of  the  uppermost  height  thereof,  or  to  the  nearest 
tier  of  beams  to  that  measurement,  in  any  building  so  constructed, 
and  every  lower  section  of  60  feet,  or  to  the  nearest  tier  of  beams  to 
such  vertical  measurement,  or  part  thereof,  shall  have  a  thickness  of 
4  inches  more  than  is  required  for  the  section  next  above  it  down  to 
the  tier  of  beams  nearest  to  the  curb  level. 


FIELD  OPERATIONS  AND 
CONCRETE  WORK 


PRELIMINARY  WORK 


DUTIES  OF  THE  SUPERINTENDENT 

1.  Reinforced-concrete  work,  to  be  constructed  econom¬ 
ically  and  rapidly,  should  be  done  under  the  direction  of  a 
competent  superintendent  or  foreman.  The  superintendent 
should  be  familiar  with  this  class  of  work  so  far  as  the  field 
management  is  concerned,  and,  in  order  to  secure  the  best 
results,  he  should  have  some  knowledge  of  the  theory  and 
practice  of  designing.  In  many  instances,  the  failure  or 
collapse  of  reinforced-concrete  structures  can  be  traced 
directly  to  superintendents  or  foremen  who  are  incompetent. 

In  addition,  the  superintendent  should  possess  executive 
ability,  so  that  the  work  will  be  carried  on  in  a  system¬ 
atic  manner.  Not  infrequently  are  the  operations  on  the 
construction  of  reinforced-concrete  structures  totally  dis¬ 
organized  simply  because  the  superintendent  is  unable  to 
systematize  thoroughly  each  step  of  the  work.  As  a  rule, 
the  operation  that  has  the  appearance  of  organization  and 
neatness  is  the  one  that  is  being  executed  at  the  least  cost  and 
with  the  greatest  despatch. 

In  the  ensuing  articles  it  is  proposed  to  give  the  information 
that  a  superintendent  or  foreman  of  reinforced-concrete  con¬ 
struction  should  possess. 


COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS*  HALL,  LONDON 


2 


FIELD  OPERATIONS  AND 


§34 


2.  Examination  and  Care  of  Drawings. — The  first 

duty  of  the  superintendent  of  reinforced-concrete  construction 
is  to  make  a  thorough  examination  of  the  plans  and  specifica¬ 
tions.  These  are  usually  in  his  possession  before  the  work  is 
commenced,  and  he  should  familiarize  himself  with  every 
detail  of  the  construction.  The  drawings  generally  show 
dimensions,  sizes,  and  amount  of  reinforcement,  as  well  as 
the  details  of  construction;  but  sometimes  they  are  only  the 
architect’s  plans,  which  are  frequently  limited  in  the  informa¬ 
tion  that  they  give.  In  such  cases,  subsequent  framing  plans, 
furnished  by  the  construction  company,  will  have  to  be  studied 
in  order  to  learn  the  details  regarding  the  distances  from  center 
to  center  of  columns,  beams,  and  girders  as  well  as  the  amount 
of  reinforcement  required  by  each  beam  and  girder  and  the 
slab  construction.  As  a  rule,  the  drawings  are  subservient 
to  the  specifications,  and  if  the  plans  and  specifications  do  not 
agree,  the  usual  practice  is  to  follow  the  specifications.  It  is 
best,  however,  if  contradictions  occur,  to  have  an  understand¬ 
ing  at  once  with  the  architect  or  engineer  controlling  the  work. 
An  intelligent  superintendent  will  frequently  find  that  some 
dimensions  are  incorrect  and  that  others  do  not  “tie  up”; 
also,  he  will  not  infrequently  find,  especially  upon  the  archi¬ 
tect’s  framing  plans,  beams  or  girders  that  are  not  properly 
reinforced.  In  such  cases,  while  he  has  no  authority  to  make 
changes  in  the  plans,  it  will  be  greatly  to  his  advantage  to 
consult  the  proper  authority  and  have  such  discrepancies 
or  mistakes  rectified  before  starting  operations. 

The  superintendent  cannot  become  familiar  with  a  com¬ 
plete  set  of  plans,  drawings,  and  specifications  at  once;  it  is 
only  after  going  over  them  many  times  that  he  can  fix  the 
entire  work  thoroughly  in  his  mind.  An  excellent  plan, 
especially  if  the  job  is  a  large  one,  is  to  photograph  the  tra¬ 
cings  and  then  mount  the  photographs  on  cardboard  so  that 
they  can  be  carried  in  the  pocket  and  studied  at  leisure.  By 
this  means,  constant  reference  may  be  made  to  the  plans, 
and  the  superintendent  will  thus  be  able  to  anticipate  the  work 
several  days  ahead  and  consequently  avoid  delays  in  the 
receipt  of  material. 


§34 


CONCRETE  WORK 


3 


3.  The  plans  should  be  filed  in  the  superintendent’s  office 
in  a  systematic  manner,  so  that  they  can  be  easily  referred  to. 
In  many  instances,  the  plans — many  of  them  missing — are 
scattered  about  in  promiscuous  rolls,  and  frequently  those 
that  are  obtainable  are  plans  that  have  not  been  revised  to 
date.  In  nearly  every  large  job  of  construction  work  it  is 
necessary  to  make  certain  revisions  of  the  plans,  and  the  care¬ 
ful  architect  or  engineer  usually  marks  such  plans  “Revised” 
and  gives  the  date  of  revision.  The  superintendent  should 
make  particular  note  of  these  revisions  and  keep  the  revised 
blueprints  with  the  originals.  In  this  way,  he  will  be  able 
to  carry  out  the  work  according  to  the  revised  plans,  and 
besides  he  will  be  able  to  tell  how  much  extra  work  will  be 
required.  It  is  best,  especially  for  a  large  job,  to  mount  all  the 
blueprints  on  linen  and  then  bind  them  so  that  none  will  be 
lost. 

4.  Organization  of  Working  Force. — The  working 
force  needed  for  reinforced-concrete  construction  is,  of  course, 
largely  influenced  by  the  extent  of  the  work.  The  superin¬ 
tendent  should  carefully  analyze  the  quantity  of  form  work 
to  be  done,  the  amount  of  bending  and  working  that  the  steel 
reinforcement  will  require,  and  the  number  of  cubic  yards  of 
concrete  that  is  to  be  placed;  he  will  then  be  able  to  form 
some  idea  of  the  number  of  men  required. 

5.  With  large  work,  it  is  necessary  to  employ  a  time¬ 
keeper,  so  that  the  superintendent’s  time  need  not  be  occu¬ 
pied  with  this  detail  of  the  work.  If  hoisting  engines  are  to 
be  used,  they  must  be  properly  manned  with  engineers,  who 
must  be  licensed  if  so  required  by  the  local  laws.  Usually, 
subordinate  to  the  superintendent  on  reinforced-concrete  jobs 
is  a  general  foreman,  who  acts  as  assistant  superintendent. 
If  the  extent  of  the  work  does  not  warrant  the  employment 
of  such  a  man,  then  there  must  be  at  least  a  carpenter  fore¬ 
man.  There  should  also  be  a  foreman  or,  at  least,  a  skilled 
mechanic  with  some  executive  ability,  in  charge  of  the  work¬ 
ing  and  bending  of  the  steel  reinforcement.  If  the  work  is 
of  considerable  area  and  the  concrete  is  to  be  placed  in 

211—15 


4 


FIELD  OPERATIONS  AND 


§34' 


several  locations  at  the  same  time,  there  should  be  a  fore¬ 
man,  or  overseer,  at  each  point  where  the  concrete  is  being 
placed.  It  is  also  advisable  to  have  a  foreman  in  charge 
of  the  concrete-mixing  plant,  for  it  is  only  by  supervising 
the  mixing  that  a  uniform  grade  of  concrete  will  be  pro¬ 
duced,  especially  if  large  quantities  of  the  material  are  to 
be  mixed. 

6.  Among  the  workmen  employed  on  the  construction, 
there  must  be  carpenters  to  erect  the  form  work.  The  num¬ 
ber  of  carpenters  needed  depends  on  the  character  and  extent 
of  the  work  and  is  influenced  by  the  question  of  their  dis¬ 
posal  when  one  set  of  forms  is  finished  and  the  concrete  is 
being  placed.  In  other  words,  it  is  economical  and  consistent 
with  good  organization  to  be  able  to  retain  the  full  complement 
of  carpenters  throughout  the  entire  job,  and  not  have  to  lay 
them  off  when  one  set  of  form  work  is  completed  and  before 
the  next  set  can  be  built. 

The  number  of  men  required  to  transfer  the  concrete  to 
the  position  where  it  is  to  be  placed  is,  of  course,  determined 
by  the  distance  that  the  concrete  has  to  be  moved.  The  men 
to  place  the  concrete  should  be  of  such  number  as  to  be  able 
to  handle  all  the  concrete  brought  by  those  engaged  in  its 
transportation.  These  men  are  laborers  and  are  paid  the 
usual  wages  for  laborers  in  the  locality  in  which  the  work  is 
carried  on.  There  are  also  several  laborers  required  at  the 
mixer  to  carry  cement,  sand,  and  broken  stone. 

7.  Lines  and  Levels. — As  with  any  construction  work, 
it  is  necessary  for  the  superintendent  to  obtain  accu¬ 
rately  the  lines  and  levels.  If  only  part  of. the  building  is  to 
be  of  reinforced  concrete  and  the  work  is  under  the  direction 
of  a  builder  to  whom  the  reinforced-concrete  superintendent 
reports,  then  the  lines  and  levels  are  usually  determined  by  the 
builder’s  foreman.  If  the  work  is  to  be  entirely  of  reinforced 
concrete,  however,  and  the  superintendent  of  the  reinforced- 
concrete  work  has  entire  charge  of  the  work,  he  is  the  one  that 
has  to  lay  out  the  lines  of  the  structure  and  to  stake  off  the 
work.  This  work  should  be  carefully  gone  over  several  times, 


§34 


CONCRETE  WORK 


5 


for  nothing  will  be  of  greater  assistance  in  the  execution  of  the 
work  than  stakes  carefully  placed  and  lines  carefully  laid. 
This  work  requires  special  care  in  connection  with  reinforced- 
concrete  construction,  because  the  steel  reinforcement  for 
the  different  beams  and  girders  is  made  up  accurately  from 
the  framing  plan,  and  a  mistake  in  the  layout  of  the  building 
will  cause  trouble  in  the  placement  of  the  steel  reinforcement 

by  giving  improper  bearings  on  the  walls  or  piers. 

/ 

8.  It  is  also  important  that  a  datum  level  be  established 
at  some  fixed  point  adjacent  to  the  building  and  that  all  the 
levels  of  the  floors  or  different  parts  of  the  structure  be  worked 
from  this  point.  These  levels  are  always  marked  on  care¬ 
fully  prepared  architectural  drawings  and  framing  plans, 
being  usually  established  from  such  point  as  the  city  datum 
at  the  curb  or  the  zero  mark  established  by  the  plans.  As  the 
work  progresses,  the  superintendent  should  carefully  check 
up  the  level  of  the  forms,  because  no  mistake  made  in  the 
levels  can  be  rectified  after  the  reinforced-concrete  work  has 
been  placed.  For  this  reason,  too  much  care  cannot  be  taken 
to  see  that  the  form  work  is  placed  so  as  to  bring  the  floors  or 
other  parts  of  the  structure  to  the  necessary  height. 


HANDLING  OF  MATERIALS 


CEMENT 

9.  After  having  reviewed  the  plans  and  specifications 
and  the  site  of  the  building,  the  first  step  to  be  taken  by  the 
superintendent  of  a  reinforced-concrete  construction  job  is  to 
have  constructed  adjacent  to  the  operation  a  frame  building 
for  the  storage  of  cement.  This  building  should  be  kept 
under  lock  and  key,  and  should  be  of  a  size  to  accommodate 
several  carloads  of  cement;  or,  if  the  operation  work  requires 
greater  quantities  of  the  material  to  be  placed  in  storage,  it 
should  be  made  larger.  As  cement,  especially  in  bags,  is 
readily  ruined  if  exposed  to  dampness,  it  should  be  taken 


6 


FIELD  OPERATIONS  AND 


§34 


directly  from  the  cars  into  the  storage  shed.  If  this  matter 
is  neglected  by  the  superintendent  or  foreman,  the  contractor 
is  liable  to  suffer  severe  loss.  If  the  ground  is  liable  to  be 
wet,  a  rough  wooden  floor  should  be  constructed  in  the  shed 
to  keep  the  bags  of  cement  dry. 

10.  The  superintendent  should  exercise  a  close  super¬ 
vision  over  the  cement  shipments.  He  must  know  from  time 
to  time  the  quantity  of  cement  on  hand  as  well  as  the  quantity 
that  is  likely  to  be  needed;  he  should  also  keep  track  of  the 
shipments  from  the  mill  and  know  about  the  time  when  the 
cars  of  cement  are  expected  to  arrive.  If  there  is  any  hauling 
to  be  done,  he  should  arrange  to  have  teams  ready  to  haul 
the  cement  from  the  cars  to  the  site  of  the  operation  or  the 
cement  storage  house. 

Cement  may  be  received  in  barrels,  duck  bags,  or  paper 
bags.  However,  it  is  not  shipped  in  barrels  unless  very  large 
quantities  are  to  be  used.  The  price  of  cement  is  always 
based  on  the  price  per  barrel  at  the  mill.  To  this  price  must 
be  added  the  freight  per  barrel  and  also  the  cost  of  the  duck 
bags,  which  is  10  cents  per  bag.  This,  however,  is  the  gross 
cost  of  the  cement,  for  the  mills  usually  allow  7\  cents  per  bag 
for  all  bags  returned,  the  purchaser  to  pay  the  freight  on  the 
bags  sent  back  to  the  mill.  The  superintendent  should 
appoint  some  one  of  his  organization  to  look  after  the  duck 
bags,  and  this  person  should  see  that  they  are  properly  sorted, 
bundled,  tagged,  and  returned. 

11.  The  standard  unit  of  measurement  for  Portland 
cement  is  the  barrel.  The  size  of  cement  barrels  varies 
considerably;  usually,  however,  the  quantity  of  Portland 
cement  contained  in  a  barrel  when  closely  packed  weighs 
approximately  376  pounds  and  the  barrel  about  20  pounds, 
making  a  total  weight  of  about  396  pounds.  In  a  barrel  of 
cement  there  is  approximately  3.6  cubic  feet;  when  this  "is 
dumped  out  loosely,  however,  it  will  make  from  4  to  5.2  cubic 
feet.  Thus,  it  can  be  readily  seen  that  if  the  cement  is 
measured  by  the  barrel,  a  richer  mixture  will  be  obtained 
than  if  the  cement  is  dumped  out  and  measured  by  means  of 


§34 


CONCRETE  WORK 


7 


small  boxes  or  measures.  Occasionally,  the  ingredients  in 
concrete  work  are  mixed  by  weight  in  order  to  avoid  such 
discrepancies  as  exist  between  the  quantity  of  cement  con¬ 
tained  in  a  barrel  when  packed  tightly  and  the  quantity  of 
cement  contained  in  a  box  or  a  measure  when  loose.  The 
number  of  cubic  feet  contained  in  a  barrel  has  been  custom¬ 
arily  taken  as  3.6,  which  would  make  1  cubic  foot  of  cement 
weigh  somewhat  more  than  100  pounds.  Broken  stone  and 
sand  weigh  about  100  pounds  to  the  cubic  foot,  so  that  if  a 
barrel  were  assumed  to  contain  3.6  cubic  feet,  the  ingredients 
would  be  proportioned  exactly  according  to  weight.  In  work 
where  great  accuracy  is  not  required,  common  practice  seems, 
therefore,  to  be  to  consider  a  barrel  as  containing  4  cubic  feet 
or  4  bags  of  cement;  thus,  each  bag  of  cement  is  counted  as 
being  equivalent  to  1  cubic  foot.  By  this  means,  a  very  con¬ 
venient  way  is  found  of  measuring  the  quantities  when  the 
cement  is  shipped  in  bags. 

The  natural  cements  are  lighter  than  the  Portlands,  some 
of  the  Western  brands  weighing  only  265  pounds  per  barrel, 
while  the  Rosendale  cements  of  New  York  weigh  about 
282  pounds.  Natural  cements  are  sold  in  duck  bags,  the 
same  as  Portland  cements,  but  3  bags  are  made  equal 
to  the  barrel. 

12.  Testing  of  Cement. — In  all  instances,  the  cement  is 
supposed  to  be  tested  at  the  mill.  Test  samples  are  taken  from 
the  several  bins  of  the  stock  in  storage,  and  when  the  cement 
has  passed  inspection,  the  material  is  taken  from  these  bins 
and  packed  for  shipment  and  delivery.  Frequently,  however, 
contractors  and  engineers  claim  that  the  mill  test  is  not 
entirely  satisfactory  and  require  that  an  additional  test  be 
made.  This  test  is  subject  to  the  approval  of  the  architect 
or  engineer,  and  is  generally  made  at  the  expense  of  the 
owner.  In  such  instances,  therefore,  the  superintendent  is 
required  to  test  all  shipments  before  using  the  cement. 
Sometimes,  of  course,  the  cement  may  be  needed  on  the  job 
before  there  is  time  to  test  it.  In  emergencies  like  this,  the 
superintendent  must  decide  whether  to  use  the  cement  without 


8 


FIELD  OPERATIONS  AND 


§34 


testing  or  to  hold  up  the  work.  If  it  is  to  be  used  without 
testing,  the  best  plan,  if  possible,  is  to  use  it  in  unimportant 
places. 

One  of  the  most  important  tests  employed  to  determine  the 
durability  of  the  cement  is  known  as  the  boiling  test.  Besides 
the  boiling  test,  tensile  tests  are  often  required  as  well.  The 
cement  mills,  however,  are  now  making  cement  of  such  quality 
and  of  such  uniform  grade  that  there  is  little  likelihood  of  it 
being  deficient  in  the  tensile  test,  either  in  the  neat  cement 
briquets  or  in  the  cement  and  sand  briquets.  Methods  of 
testing  cement  are  described  at  length  in  Tests  on  Cement. 


MISCELLANEOUS  MATERIALS  USED  IN  CONCRETE  WORK 

13.  Care  of  Stone,  Sand,  and  Gravel. — The  prin¬ 
cipal  care  to  be  exercised  in  the  handling  of  stone,  sand,  and 
gravel  is  to  see  that  none  is  contaminated  with  dirt  or  foreign 
substances.  These  materials  should  also  be  protected  from 
intense  heat  in  summer  and  from  freezing  weather  in  winter. 
In  large  operations,  they  are  generally  stored  in  open  sheds 
or  in  covered  bins.  These  storage  places  usually  have  a  rough 
wooden  floor,  so  that  there  will  be  no  danger  of  shoveling  up 
some  of  the  soil  and  carrying  it  into  the  mixer. 

If  the  materials  have  been  subjected  to  the  heat  of  the  sun, 
they  are  liable  to  cause  trouble  in  the  mixer  by  tending  to 
cake  the  cement.  In  the  summer  time,  therefore,  care  should 
be  taken  to  wet  the  stone  down  frequently  and  to  protect  the 
sand  and  gravel  from  the  heat.  In  winter,  it  is  well  to 
prevent  the  stone,  sand,  and  gravel  from  becoming  wet  and 
from  having  the  moisture  in  them  frozen,  because  frost  is 
detrimental  to  the  concrete.  When  there  are  indications  that 
the  stone,  sand,  and  gravel  have  been  frozen,  means  should 
always  be  taken  to  thaw  them  out,  either  by  forming  a  hollow 
in  the  material  and  building  a  fire  therein,  or  by  putting  it 
in  a  sheet-metal  pan  under  which  a  fire  is  lighted. 

14.  Care  and  Infection  of  Steel  Reinforcement. 

The  steel  reinforcement  to  be  used  in  concrete  construction 


§34 


CONCRETE  WORK 


9 


should  be  stored  in  such  a  way  that  bundles  of  bars  of  the 
same  size,  will  be  kept  together  on  racks  or  in  piles.  If  the 
material  that  has  been  carefully  ordered  from  the  drawings, 
as  well  as  certain  lengths  of  bars  intended  for  certain  positions 
in  the  work,  are  delivered  in  such  a  way  as  not  to  indicate 
where  they  are  to  be  used,  the  superintendent  should  have 
them  carefully  sorted  and  then  marked  or  tagged  to  corre¬ 
spond  with  the  marks  on  the  drawings.  It  is  advisable  always 
to  do  this  before  the  bars  are  needed  for  bending,  working,  or 
placing  in  the  forms;  and,  where  space  is  available,  as  much 
care  should  be  taken  of  the  storage  of  the  reinforcing  steel  as 
of  the  other  materials. 

The  superintendent  should  carefully  inspect  the  shipments 
to  see  that  the  bars  are  not  badly  rusted,  and  if  rust  has 
accumulated  in  quantity,  he  should  have  it  cleaned  off  with 
a  steel  brush.  If  care  is  not  exercised  in  sorting  bars  that  have 
been  ordered  according  to  the  plans,  it  will  frequently  be  found 
that  bars  of  certain  lengths  have  been  cut  for  positions  in 
which  shorter  bars  were  required,  and  that  upon  the  final 
operations  of  the  building  there  is  no  steel  reinforcement  of 
sufficient  length  on  hand  to  finish  the  work.  This  is  par¬ 
ticularly  true  where  expanded  metal,  which  comes  in  sheets 
of  certain  size,  is  employed  for  reinforcing  floor  slabs.  If 
these  sheets  are  not  properly  sorted  for  placing  in  the  correct 
position,  there  will  be  extravagant  laps  in  many  places,  and 
when  the  steel  reinforcement  for  the  top  story  of  the  building 
or  the  final  operation  in  the  structure  is  about  to  be  placed, 
it  will  be  found  to  be  too  short  for  the  spans  and  that  a 
great  bulk  of  the  steel  has  been  wasted.  The  careful  sort¬ 
ing  out  of  the  steel  reinforcement  not  only  tends  to  pro¬ 
mote  economy,  but  also  largely  assists  and  facilitates  the 
work  when  it  is  necessary  to  commence  the  operation  of 
bending  and  assembling. 

A  list  should  be  kept  of  all  the  steel  reinforcement  on  the 
job,  and  as  the  various  pieces  are  taken  from  the  stock,  they 
should  be  checked  off.  The  light  reinforcement,  such  as  the 
stirrups  and  the  wire  ties,  may  be  delivered  in  stock  lengths 
and  cut  up  as  desired. 


10 


FIELD  OPERATIONS  AND 


§34 


15.  Care  of  Dumber  for  Form  Work. — The  finish  of 

the  reinforced-concrete  construction  depends  largely  on  the 
kind  of  lumber  used  in  the  forms.  Therefore,  the  lumber 
for  this  purpose  should  not  only  be  well  seasoned,  but  when 
delivered  should  be  properly  protected.  Frequently  the 
superintendent  is  compelled  to  use  old  material  for  the  form 
construction;  that  is,  material  that  has  been  previously  used 
in  reinforced-concrete  work.  Such  lumber  is  often  badly  split 
and  splintered,  in  which  case  it  will  be  well  to  have  several 
carpenters  patch  up  the  lumber  and  get  it  into  good  shape 
previous  to  constructing  the  forms.  Although  the  appearance 
of  the  concrete  construction  is  not  always  a  criterion  of  its 
strength,  it  usually  follows  that  if  the  work  shows  a  finished 
appearance  and  the  beams,  girders,  and  columns  are  level 
and  plumb,  care  has  also  been  used  in  placing  the  steel  and 
concrete  and  the  strength  of  the  structure  insured. 


DEVICES  USED  IN  CONCRETE 
CONSTRUCTION 


CONCRETE  MIXERS 


SELECTION  OF  MIXER 

16.  In  the  construction  of  a  reinforced-concrete  structure, 
the  quantity  of  concrete  to  be  placed  decides  the  amount  of 
equipment  and  the  character  of  the  machinery  that  is  to  be 
employed.  The  character  of  the  work  also  influences  these 
two  factors.  In  all  instances,  the  concrete  plant  should  be 
equipped  with  machinery  suitable  for  the  size  of  the  work 
and  the  number  of  men  that  will  be  available  in  the  construc¬ 
tion  operation.  On  small  work,  the  concrete  is  frequently 
mixed  by  hand;  it  is,  however,  unusual  for  the  concrete  in 
large  operations  to  be  so  mixed.  The  successful  contractor 
will  employ  the  mixing  machine  that  is  found  most  efficient 
and  will  give  careful  attention  to  its  erection  in  the  field. 


§34 


CONCRETE  WORK 


11 


17.  There  are  many  kinds  of  concrete  mixers  in  com¬ 
mercial  use.  These  mixers  are  classified  according  to  the 
principles  upon  which  they  operate,  and  are  known  as  batch 
mixers ,  continuous  mixers,  and  quantitative  mixers. 

Frequently,  the  selection  of  the  mixer,  especially  in  work 
where  new  equipment  is  to  be  used,  is  left  to  the  superintend¬ 
ent.  In  making  the  selection,  the  superintendent  should 
bear  in  mind  the  character  of  the  work;  that  is,  whether  it  is 

i  * 

of  more  importance  to  turn  out  great  quantities  of  concrete 
than  it  is  to  have  a  uniform  mixture,  or  whether,  as  in  a 
reinforced-concrete  building,  the  most  important  considera¬ 
tion  is  to  have  concrete  delivered  from  the  mixer  in  uniform 
consistency.  Usually,  for  heavy  mass  work  the  continuous 
mixer  is  advantageous,  but  the  batch  mixer  is  now  more 
used  for  work  such  as  that  included  in  ordinary  reinforced- 
concrete  buildings. 


BATCH  MIXERS 

18.  Cube  Mixers. — One  of  the  oldest  and  best  known 
forms  of  batch  mixer  is  the  cube  mixer.  It  consists  essen¬ 
tially  of  a  cubical  steel  box  revolving  on  a  hollow  horizontal 
shaft  that  passes  through  diagonally  opposite  corners.  This 
box  is  charged  and  discharged  through  a  trap  door  placed  near 
one  of  its  corners.  In  operation,  the  mixer  is  revolved  until 
the  corner  where  the  door  is  located  comes  uppermost;  then 
the  door  is  opened  and  the  ingredients  are  dumped  through  a 
chute,  or  hopper,  into  the  mixer.  The  door  is  then  closed  and 
the  box  is  revolved.  After  a  few  turns  to  mix  the  materials, 
the  necessary  water  is  introduced  through  the  hollow  shaft, 
and  then  the  revolving  is  continued  for  some  time,  after  which 
the  box  is  stopped,  with  the  door  at  the  lowest  corner.  The 
door  is  then  opened  and  the  mixed  concrete  is  dumped  into 
a  car  or  other  receptacle  and  taken  away. 

The  usual  size  of  the  cube  is  4  feet  on  each  edge.  This  size 
has  a  nominal  capacity  of  1  cubic  yard  of  rammed  concrete. 
The  ingredients  would  fill  the  mixer  about  half  full.  With  a 
larger  charge,  the  concrete  may  not  be  thoroughly  mixed. 
In  using  this  mixer,  care  should  be  taken  to  keep  it  clean  and 


12 


FIELD  OPERATIONS  AND 


§34 


to  prevent  accumulations  of  particles  of  mortar  in  the  corners 
or  on  projections  inside  the  cube.  This  can  be  done  by 
pounding  energetically  on  the  outside  of  the  cube  with  a 


- - - -  *  wU  -k  — 


I-'*  1* 


Fig.  1 


wooden  mallet  as  each  batch  is  dumped  out;  the  clinging 
particles  of  mortar  are  thus  detached  before  they  have  time 
to  stick  fast. 


§34 


CONCRETE  WORK 


13 


19.  A  cube  mixer  is  usually  mounted  upon  a  substantial 
framework  of  timber,  as  illustrated  in  Fig.  1,  which  shows  a 
Carlin  cube  mixer.  The  cube  is  driven  by  a  belt  a,  and 
gears  b  serve  to  reduce  the  speed  of  rotation.  The  cube  is 
shown  in  the  position  it  occupies  when  being  filled.  The  trap 
door  for  filling  and  discharging  is  shown  open  and  swung  back 
at  c.  The  hopper  above  the  cube  is  made  in  two  parts.  The 
lower  part  is  hung  from  one  of  the  posts  of  the  platform,  as 
shown.  When  the  cube  is  revolving,  this  lower  part  can  be 
swung  out  of  the  way.  At  d  is  shown  the  water  tank 
which  feeds  water  into  the  cube  through  the  pipe  e.  Below 
the  cube  is  shown  a  car  f  into  which  the  finished  concrete  is 
dumped. 

If  the  nature  of  the  work  is  such  that  the  ingredients  can 
be  easily  taken  to  the  platform  above  the  cube,  this  machine 
will  be  found  economical,  because  after  the  materials  are 
once  shoveled  into  the  hopper  above  they  do  not  have  to 
be  handled  again  until  the  concrete  is  deposited  in  the  con¬ 
veying  car. 

20.  The  capacity  of  a  cube  mixer  varies  according  to 
the  volume  of  the  charge  and  the  time  interval  between  suc¬ 
cessive  batches.  Various  sizes  of  charges  and  various  rates 
of  speed  have  been  used  by  different  engineers,  ranging  from 
a  charge  sufficient  to  produce  18  cubic  feet  of  rammed  con¬ 
crete  to  one  producing  27  cubic  feet,  and  from  a  speed  of  G  to 
one  of  14  revolutions  per  minute.  The  number  of  charges  per 
hour  will  vary  according  to  the  speed  of  revolution  of  the 
mixer.  This,  however,  should  not  be  great  enough  to  prevent 
by  centrifugal  force  the  action  of  gravity  from  causing  the 
ingredients  to  tumble  or  roll  over  as  the  box  revolves. 

The  following  conditions  have  been  found  to  produce  excel¬ 
lent  results  with  a  4-foot  cube  mixer:  Each  batch  is  mixed 
1  £  minutes  at  a  speed  of  1 0  revolutions  per  minute,  making  a 
total  of  15  turns  per  batch.  The  time  allowed  for  dumping, 
cleaning,  and  charging  the  mixer  and  for  temporary  stoppage 
of  the  work  is  about  34  minutes,  making  an  average  time 
interval  between  successive  batches  of  5  minutes,  which  is  at 


14 


FIELD  OPERATIONS  AND 


§34 


the  rate  of  twelve  batches  per  hour.  Allowing  only  J  cubic 
yard  of  rammed  concrete  per  batch,  this  gives  for  a  10-hour 
day  an  output  of  105  cubic  yards. 

21.  Ransome  Mixer. — Another  form  of  batch  mixer 
called  the  Ransome  mixer  is  illustrated  in  two  views  in  Fig.  2. 

This  machine  consists 
essentially  of  a  hol¬ 
low  cylindrical  drum 
that  is  mounted  on  a 
horizontal  axis  and 
has  a  circular  opening 
in  each  end.  As 
shown  in  (a),  the 
mixer  is  charged 
through  one  of  these 
openings  a.  In  the 
other  opening,  shown 
in  ( b ),  is  a  chute  b 
that  receives  the 
mixed  concrete  from 
the  drum  and  delivers 
-it  to  a  wheelbarrow 
or  other  receptacle. 
Inside  the  drum  are 
several  steel  blades 
arranged  in  such  a 
manner  as  to  deflect 
the  material  from 
side  to  side  as  the 
drum  revolves.  The 
drum  is  mounted  on  four  rollers  and  is  supported  on  a  truck, 
which  is  either  made  stationary  or  mounted  on  wheels,  as 
required.  The  mixer  is  turned  by  power  applied  to  the  rim  of 
the  drum  either  from  an  engine  mounted  on  the  same  frame 
or  from  a  belt  or  a  chain. 

The  process  of  mixing  is  as  follows:  The  required  quantity 
of  water  for  a  batch  is  first  placed  in  the  mixer;  then  the 


§34 


CONCRETE  WORK 


15 


cement,  sand,  and  broken  stone,  previously  measured,  are 
dumped  in  as  the  drum  revolves. 

The  chute  b ,  Fig.  2  (6),  through  which  the  mixer  discharges, 
is  kept  in  the  position 
shown  in  Fig.  3  (a) 
while  the  concrete  is 
being  mixed.  When 
it  is  time  to  empty 
the  mixer,  the  handle 
c ,  Fig.  2,  is  turned. 

This  turning  of  the 
handle,  which  is  con¬ 
nected  to  the  chute 
by  means  of  a  chain, 
as  shown,  tips  the 
chute  b,  as  illustrated 
by  dotted  lines  in  the 
figure.  Meanwhile, 
the  drum  is  revolving 
and  lifting  masses  of 
concrete  up  one  side 
in  the  direction  of 
its  motion.  These 
masses  finally  fall  by 
the  action  of  gravity 
to  the  bottom  of  the 
drum. 

The  path  followed 
by  the  concrete  in 
the  mixer  is  shown 
diagrammatically  in 
Fig.  -3  ( b ).  The 

blades  are  represent¬ 
ed  by  short  radial 
lines.  When  the 
chute  is  tipped  down,  as  shown  by  dotted  lines  in  Fig.  2  (6), 
the  upper  end  intercepts  the  flow  of  concrete,  as  shown  in  Fig.  3 
(6),  and  the  mass  slides  down  the  chute  and  out  of  the  drum. 


16 


FIELD  OPERATIONS  AND 


§34 


The  Ransome  mixer  is  made  in  several  sizes,  with  capacities 
varying  from  7  to  80  or  more  cubic  yards  per  hour. 


22.  Gilbreth  Rotary  Mixer. — In  Fig.  4  is  shown  a 
Gilbreth  rotary  mixer.  This  mixer  differs  from  the  Ran¬ 
some  in  that,  instead  of  having  a  chute  for  feeding  or  dis¬ 
charging  the  concrete,  it  is  made  so  that  a  wheelbarrow  can 
be  put  directly  inside  the  drum.  The  mixer  can  be  fed  or 
discharged  from  either  side.  The  inside  is  fitted  with  heavy 
steel  veins,  or  shovels,  that  carry  about  1  cubic  foot  of 


concrete  apiece  to  the  top  of  the  mixer  and  there  let  it  drop 
into  the  mass  below  or  into  the  wheelbarrow.  This  mixer 
is  made  in  various  sizes  to  produce  concrete  at  desired 
rate  to  suit  different  conditions. 


23.  Smith  Mixer. — In  Fig.  5  is  illustrated  the  Smith 
mixer.  This  machine  is  self-contained  and  portable,  the 
mixer,  engine,  and  boiler  being  mounted  together  on  a  truck, 
which  is  supported  on  wheels.  The  machine  consists  of  a 


§34 


CONCRETE  WORK 


17 


drum  of  double  conical  form  that  is  supported  and  guided  by 
a  frame  that  can  be  tilted  at  will  while  the  drum  is  revolving. 
The  two  conical  sides  of  the  mixer  are  connected  at  their  bases 
to  a  central  ring,  which  is  provided  with  gear-teeth  for  revolv¬ 
ing  the  drum  as  well  as  machined  surfaces  for  guiding  it. 
The  conical  sides  are  truncated,  having  circular  openings  at 
their  ends  for  the  reception  and  discharge  of  the  material. 
The  ingredients  are  fed  in  at  one  end  of  the  drum,  and  after 
the  required  number  of  revolutions  the  mixed  concrete  is 


discharged  at  the  other  end  by  tilting  the  drum  while  it  is 
running  at  full  speed.  The  interior  of  the  drum  is  provided 
with  blades  arranged  so  as  to  insure  thorough  mixing.  The 
mixer  is  made  in  various  sizes  with  various  capacities  to  suit 
different  conditions  of  work. 


24.  International  Concrete  Mixer. — Fig.  6  illus¬ 
trates  the  International  concrete-manufacturing 
apparatus.  The  mixer,  which  is  somewhat  similar  to  the 
Ransome  mixer,  is  shown  at  a.  This  apparatus  is  designed 
to  handle  the  concrete  from  the  time  the  ingredients  are 


18 


Fig 


§34 


CONCRETE  WORK 


19 


proportioned  to  the  time  the  finished  concrete  is  dumped 
into  the  car,  ready  to  be  hauled  to  the  work  and  put  in 
place.  The  measured  ingredients  are  dropped  into  the  car  b, 

•  which  is  then  hauled  up  the  plane  by  the  engine  shown 
at  c.  As  the  car  ascends,  the  front  wheels,  which  are  of  nar¬ 
rower  gauge  than  the  hind  wheels,  run  on  a  track  on  the 
horizontal  girt,  while  the  hind  wheels  on  the  outside  tracks 
continue  up  the  plane.  In  this  way,  the  car  is  brought  into 
the  position  shown  by  dotted  lines  in  the  figure,  and  the  con¬ 
tents  of  the  car  slides  out  into  the  hopper  df  and  thence  into 
the  mixer  itself.  The  engine  runs  the  mixer  continuously. 
The  hoist  that  hauls  up  the  cars  is  operated  by  the  lever  e. 
When  it  is  desired  to  elevate  the  car,  this  lever  is  thrown  over 
so  as  to  operate  a  clutch  driven  by  the  two  miter  wheels  shown 
at  /.  When  the  car  reaches  the  position  shown  by  the  dotted 
lines,  the  clutch  is  thrown  out,  but  the  car  is  held  by  the  oper¬ 
ator  putting  his  foot  on  the  lever  g,  which  operates  a  band 
brake,  on  the  hoisting  drum,  not  shown  in  the  cut.  When  it 
is  desired  to  lower  the  car,  the  operator  takes  his  foot  off 
the  lever  g,  and  thus  permits  the  car  to  descend.  To  keep  the 
car  clean,  so  that  it  will  dump  quickly,  no  water  is  added. 
The  water  goes  direct  to  the  mixer  from  a  barrel  h.  The  man 
who  receives  the  mixed  concrete  in  the  car  k  tips  the  chute  l 
by  means  of  the  handle  m,  as  explained  in  connection  with  the 
Ransome  mixer. 


CONTINUOUS  MIXERS 

25.  Principle  of  tlie  Continuous  Mixer. — The  prin¬ 
ciple  of  the  operation  of  a  continuous  concrete  mixer  is  to 
feed  into  one  end  of  the  machine  a  steady  stream  of  raw 
material  and  turn  out  mixed  concrete  at  the  other  end. 
Theoretically,  this  is  an  ideal  arrangement,  but  in  practice 
it  is  difficult  to  maintain  uniformity  in  the  grade  of  concrete 
turned  out  without  the  aid  of  some  special  measuring  appa¬ 
ratus.  If  the  stream  of  cement,  sand,  and  stone,  together 
with  the  necessary  water,  is  fed  into  the  mixer  in  the  proper 
proportions,  the  resulting  product  will  be  a  good  grade  of 

concrete.  If,  however,  there  are  variations  in  the  supply  of 

211—16 


20 


FIELD  OPERATIONS  AND 


§34 


the  ingredients,  there  will  be  corresponding  variations  in  the 
resulting  concrete,  which  at  one  time  may  be  rich  in  cement 
and  at  another  time  deficient  in  the  same  ingredient.  If  the 
ingredients  are  measured  out  in  the  proper  proportions  and  . 
fed  into  the  mixer  in  a  proper  manner,  a  good  continuous 
mixer  will  turn  out  as  good  a  quality  of  concrete  as  it  obtained 
from  batch  mixers.  Manufacturers  of  continuous  mixers 
have  realized  the  necessity  of  such  uniform  distribution  of  the 
ingredients,  and  some  of  the  leading  types  of  continuous 
mixers  are  provided  with  measuring  and  feeding  devices  to 
accomplish  this  purpose. 

26.  Drake  Mixer. — One  of  the  best  known  forms  of 
continuous-mixing  machines  is  the  Drake  mixer.  This 
mixer  consists  of  an  open  trough  fitted  with  a  longitudinal 

shaft,  to  which  are  fas¬ 
tened  blades,  or  paddles, 
some  of  which  are  set  at 
an  inclination,  so  that 
they  will  not  only  mix 
the  ingredients,  but  also 
feed  the  mixture  toward 
the  discharge  end.  The 
mixer  is  so  set  that  the 
shaft  revolves  on  a  hori¬ 
zontal  axis.  The  ingre¬ 
dients  are  deposited  by 
wheelbarrows  or  from  a 
measuring  box  at  the 
upper,  or  feeding,  end 
of  the  trough.  The 
straight  blade,  or  knife, 
at  that  end  cuts  or  stirs 
the  mass,  which  is  then  turned  over  by  the  adjacent  curved 
blade,  or  scoop,  and  advanced  to  the  next  knife,  where  it  is 
again  cut  and  then  turned  over  by  the  next  scoop,  and  so 
passed  on.  This  process  is  repeated  until  the  end  of  the 
trough  is  reached,  when  the  material  is  pushed  out  and  falls 


§34 


CONCRETE  WORK 


21 


into  a  receptacle  as  mixed  concrete.  The  ingredients  are 
mixed  dry  for  about  one-half  the  length  of  the  trough,  and 
then  a  spray  from  water  pipes  wets  the  material  as  it  is  cut 
and  turned  over.  Various  sizes  are  made,  each  mixer  having 
a  capacity,  'as  stated  by  the  makers,  of  from  75  to  200  cubic 
yards  of  concrete  per  day,  according  to  the  size. 

Fig.  7  shows  a  Drake  mixer  of  usual  design.  The  ingre¬ 
dients  are  dumped  in  at  the  far  end,  and  when  they  are  entirely 
mixed  are  delivered  down  the  chute.  The  Drake  mixer  is 
made  in  various  styles.  The  more  elaborate  ones  have  belt 
conveyers  attached  to  the  machine  to  deliver  the  ingredients 
and  take  away  the  finished  concrete.  Some  are  built  direct- 


Fig.  8 


connected  to  an  engine,  and  others  are  made  to  be  driven  with 
a  belt  or  a  chain,  as  illustrated.  Some  machines  are  portable, 
and  others  are  made  to  be  kept  in  one  place,  but  they  all  have 
the  characteristic  horizontal  shaft  with  paddles  on  it. 

27.  Cockburn  Mixer. — Another  type  of  continuous 
mixer,  called  the  Cockburn  mixer,  is  illustrated  in  Fig.  8. 
This  machine  consists  essentially  of  a  long  box  of  square  cross- 
section,  mounted  on  a  substantial  iron  frame  or  truck  and 
revolving  on  a  longitudinal  axis  on  friction  rollers,  as  shown. 
The  axis  of  the  box  is  inclined  slightly  from  the  horizontal, 
and  the  box  is  revolved  by  spur  gearing,  the  power  being 
applied  at  the  upper  end.  The  ingredients  are  fed  in  through 


22 


FIELD  OPERATIONS  AND 


§34 


a  hopper,  or  chute,  at  the  upper  end,  and  as  the  mixer  revolves 
the  material  moves  by  gravity  toward  the  lower  end,  becoming 
well  mixed  by  several  turnings  in  its  passage  and  being  finally 
discharged  in  the  form  of  concrete. 

The  Cockburn  mixer  is  about  the  oldest  type  of  continuous 
mixer  now  made;  it  has  been  used  satisfactorily  on  concrete 
work  of  considerable  magnitude.  The  volume  of  its  output 
depends  largely  on  the  rapidity  with  which  the  ingredients 


»  ill 


Fig.  9 


are  fed  into  the  mixer.  Machines  of  varying  capacities  are 
made  to  suit  the  various  demands  for  output  that  may 
be  required. 

28.  Portable  Gravity  Mixer. — In  Fig.  9  is  illustrated 
a  continuous  mixer  known  as  the  portable  gravity  mixer. 
This  mixer  consists  of  a  long  inclined  box,  or  chute,  sur¬ 
mounted  by  a  hopper  for  receiving  the  materials.  The  box 
contains  at  intervals  in  its  length  a  number  of  steel  pins  and 


§34 


CONCRETE  WORK 


23 


deflectors  that  interfere  with  the  free  passage  of  the  ingredients 
and  cause  them  to  mix.  Water  is  fed  through  a  spray  pipe 
about  midway,  this  arrangement  allowing  the  materials  to 
be  mixed  dry  in  the  upper  half  and  wet  in  the  lower  half. 


There  is  also  another  spray  pipe  at  the  top  of  the  mixer,  so 
that  if  desired  the  concrete  can  be  mixed  wet  from  the 
very  beginning 

In  operation,  the  proper  quantities  of  stone,  sand,  and 
cement  are  spread  on  the  platform  in  successive  layers,  the 


24 


FIELD  OPERATIONS  AND 


§34 


stone  being  at  the  bottom.  These  materials  are  then  shoveled 
into  the  hopper  of  the  machine,  whence  they  slide  down  the 
chute,  being  diverted  from  side  to  side  by  the  deflectors  and 
the  steel  pins. 

29.  Fig.  10  shows  one  of  these  mixers  in  detail.  As  will 
be  observed,  the  deflecting  rods  in  the  row  at  the  end  of  the 
receiving  hopper  are  placed  closer  together  than  anywhere 
else  in  the  machine.  This  is  done  to  make  sure  that  any  piece 
of  broken  stone  that  can  pass  these  bars  in  the  hopper  will  not 
clog  the  mixer.  The  bottom  of  the  mixer  is  provided  with  a 
door  a,  which  is  kept  closed  by  an  attendant  when  there  is  no 
car  underneath.  The  same  man  has  under  his  control  the 
water,  which  is  added  to  the  mixture  by  handling  the  levers  b 
and  c ;  these  levers  govern  the  flow  of  water  at  the  top  and  at 
the  middle  of  the  mixer,  respectively. 

This  type  of  concrete  mixer,  in  which  the  work  is  done  by 
gravity,  seems  to  be  well  suited  for  places  where  steam  or 
other  power  is  not  readily  available.  On  account  of  its  port¬ 
ability  and  ease  of  operation,  this  mixer  should  be  well  adapted 
for  concrete  work  around  mines  and  in  mountainous  regions 
where  the  cost  of  transportation  would  prohibit  the  use  of 
heavy  machinery  for  this  purpose. 


QUANTITATIVE  MIXERS 

30.  Quantitative  mixers  are  mixers  that  measure 
as  well  as  mix  the  ingredients  used  to  make  concrete.  They 
usually  consist  of  continuous  mixers  similar  to  those  just 
described,  to  which  is  added  a  device  for  measuring  auto¬ 
matically  the  cement,  sand,  and  broken  stone  as  it  enters 
the  mixer.  One  drawback  to  the  quantitative  mixer  for 
reinforced  concrete  buildings  is  that  it  is  often  difficult  for 
the  engineer  to  determine  exactly  what  mixture  is  being 
made.  Most  of  the  mixers  are  set  to  make  a  certain  con¬ 
crete,  as  a  1-3-6  or  a  1-2-4  mixture.  These  proportions 
are  liable  to  be  changed  either  by  tampering  with  the 
machine  or  by  using  different  qualities  of  sand  or  stone.  For 


CONCRETE  WORK 


25 


this  reason,  the  quantitative  mixer  has  been  little  used. 
Nevertheless,  with  conscientious  and  intelligent  handling,  the 
quantitative  mixer  should  be  a  valuable  labor-saving  device 
in  the  manufacture  of  concrete.  Sometimes  the  rpeasuring 
apparatus  and  mixer  proper  are  built  as  one  machine,  and 
sometimes  the  measuring  apparatus  is  built  separate,  so  that 
it  may  be  used  with  any  suitable  mixer. 


31.  Gilbretli  Measurer  and  Feeder. — A  machine 
that  can  be  applied  to  any  continuous  mixer  is  the  Gilbretli 


Fig.  11 


accurate  measurer  and  feeder.  In  works  of  great 
magnitude,  this  machine  will  be  found  economical.  Cement, 
sand,  and  broken  stone  are  dumped  into  three  storage  bins. 
The  machine  controls  the  supply  of  materials  from  each  bin 
in  such  a  manner  that  they  come  out  in  the  desired  propor¬ 
tions.  Fig.  1 1  shows  a  view  of  this  measurer.  At  a  are  shown 
the  bottoms  of  the  three  storage  bins,  which  are  built  hopper¬ 
shaped.  In  one  of  these  bins  is  stored  cement,  in  another 
sand,  and  in  the  third,  broken  stone.  These  bins,  as  already 


26 


Fig.  12 


§34 


CONCRETE  WORK 


27 


stated,  are  hopper-shaped,  but  have  no  flat  bottoms.  They 
are  closed  at  the  bottom  by  the  cylinder  c,  which  is  of  sufficient 
diameter  to  act  as  a  practically  flat  bottom  to  the  bin.  In 
the  front  of  each  hopper  there  is  a  door  b  that  may  be 
adjusted  by  a  weight,  as  shown  in  the  figure.  The  cylin¬ 
der  c  is  turned  by  a  man  at  the  handle  d.  As  the  cylinder 
revolves,  it  carries  with  it  a  layer  of  cement,  sand,  and  broken 
stone.  The  amount  of  each  material  carried  forwards,  or, 
in  other  words,  the  depth  of  each  material  on  the  cylin¬ 
der,  is  controlled  by  adjusting  the  gate  at  b.  As  the  wheel 
revolves,  the  materials  finally  slide  off  into  a  conveyer  or 
directly  into  the  mixer.  The  faster  the  operator  revolves  the 
cylinder,  the  more  materials  he  will  discharge,  but  they  will 
always  be  discharged  in  the  same  proportion. 


POWER  EQUIPMENT  FOR  MIXERS  v 

32.  A  concrete  mixer  may  be  operated  by  a  steam  engine, 
a  gas  engine,  or  an  electric  motor;  also,  where  water-power 
is  available,  it  can  be  operated  by  an  impulse  wheel  or  by 
a  turbine;  or,  if  power  is  available  from  shafting  in  an  adja¬ 


cent  building,  the  mixer  may  be  operated  by  a  chain  or 
belt  drive. 

In  Fig.  12  is  shown  a  Ransome  mixer  of  somewhat  different 
design  from  the  one  shown  in  Fig.  2  arranged  with  a  vertical 


28 


FIELD  OPERATIONS  AND 


§34 


steam  engine  and  a  vertical  boiler  supported  on  the  same 
frame  as  the  mixer.  As  shown,  the  engine  drives  the  mixer 
through  a  train  of  spur  gears. 


Fig.  14 


In  Fig.  13  is  shown  the  method  of  driving  the  Ransome 
mixer  by  means  of  a  kerosene  engine  mounted  on  the  same 
skids.  In  this  instance,  the  mixer  is  driven  from  a  reduction 
gear  that  is  connected  to  the  kerosene  engine  by  means  of  a 
belt  or  silent  chain  drive  a. 

The  layout  of  a  mixer  to  be  driven  by  an  electric  motor  is 
shown  in  Fig.  14.  Here,  as  with  the  steam  engine,  the  motor 
is  geared  to  the  reduction  gearing,  which,  in  turn,  transmits 
the  power  to  the  drum  of  the  mixer. 


If  the  mixer  is  to  be  operated  by  a  belt  or  chain  drive  from 
an  adjacent  shaft,  the  mixer  should  be  mounted  upon  skids 
in  the  manner  shown  in  Fig.  15. 


§34 


CONCRETE  WORK 


29 


From  Figs.  12,  13,  and  14  it  will  be  observed  that  the  mixer 
and  its  power  may  be  mounted  upon  the  same  skids.  These 
skids  are  often  placed  on  wheels  so  that  the  apparatus  can  be 
readily  hauled  from  one  point  to  the  other  at  the  operation 
or  for  a  considerable  distance  over  ordinary  roads. 


IIAND-CART  MIXERS 

33.  If  a  moderately  small  quantity  of  concrete  is  to  be 
used,  a  hand-cart  mixer  can  be  conveniently  employed. 
In  Figs.  16,  17,  and  18  is  shown  a  Kansome  hand  concrete 


Fig.  16 


mixer  in  different  stages  of  operation.  As  will  be  seen  from 
the  illustrations,  this  device  consists  of  a  cart  and  a  mixing 
hood.  This  hood  is  arranged  to  fit  over  the  top  of  the  cart 
and  clamp  to  it.  The  axle  of  the  cart  can  be  attached  to  the 
gearing  fixed  to  the  frame. 

In  Fig.  16  is  shown  the  cart  containing  the  proper  propor¬ 
tion  of  stone,  sand,  and  cement  about  to  be  placed  upon  the 
platform  of  the  mixing  device.  After  the  cart  is  wheeled  to 
the  mixing  frame,  water  is  added  and  the  hood  is  lowered  over 
the  cart  (see  Fig.  17)  and  clamped  in  position.  Connection 
is  made  between  the  spur  gear  and  the  axle  of  the  cart,  when 


30 


FIELD  OPERATIONS  AND 


§34 


the  contents  of  the  mixer  is  mixed,  as  shown  in  Fig.  18,  by 
revolving  the  cart  body,  and  its  contents  by  hand.  A  suffi¬ 


ciently  good  mixture  is  obtained  in  15  revolutions.  After  the 
concrete  is  mixed,  the  hood  is  raised  clear  of  the  cart  by  a 


Fig.  18 


§34 


CONCRETE  WORK 


31 


foot-lever,  shown  at  a,  Fig.  17,  and  the  cart  is  wheeled  to  the 
place  where  the  concrete  is  to  be  deposited. 

Two  men  can  readily  operate  the  mixer.  However,  where 
the  quantity  of  the  concrete  to  be  made  is  considerable,  a 
small  gas  engine  or  a  small  electric  motor  can  be  geared 
so  as  to  operate  several  of  the  frames  at  one  time.  By  hand, 
two  men  can  mix  a  batch  of  from  4  to  G  cubic  feet  of  material 
in  2  minutes,  including  the  time  of  clamping  on  the  hood  and 
removing  it.  If  the  average  batch  is  5  cubic  feet  of  loose 
material,  this  would  equal  3  cubic  feet  of  solid  concrete,  or 
9  cubic  yard  per  batch  for  each  cart  mixer  used.  The  manu¬ 
facturers  of  this  mixer  claim  that  the  total  cost,  when  three 
men  are  loading  material  into  the  cart,  two  men  mixing,  and 
one  man  wheeling,  placing,  and  spreading,  is  30  cents  per 
cubic  yard. 


OPERATION  OF  MIXERS 

34.  The  superintendent  or  foreman  of  a  reinforced-con- 
crete  job  should  take  good  care  of  the  machinery  in  his  charge. 
It  is  well  for  him  to  obtain  from  the  manufacturers  writ¬ 
ten  directions  as  to  the  use  and  operation  of  their  machines. 
Usually,  these  directions  are  explicit  and  are  based  on  experi¬ 
ence  with  the  particular  machine  in  question.  As  an  example, 
the  directions  published  by  the  Ransome  Machinery  Company 
are  given  in  part  as  follows: 

35.  Rules  for  Operating  a  Mixer. — If  the  machine 
is  mounted  on  wheels,  see  that  the  weight  is  first  taken  off 
the  wheels  and  carried  on  suitable  sills,  as  shown  in  Fig.  19. 
The  points  of  support  should  be  beneath  each  of  the  roller 
shafts,  beneath  the  bed  of  the  engine,  and  beneath  the  boiler. 
The  mixer  frame  should  be  carefully  leveled  in  both  directions. 
Remove  the  hook  bolts  that  hold  the  drum  to  the  frame. 
Fill  all  grease  and  oil  cups  and  grease  carefully  the  traction 
rings  and  roller  faces.  See  that  in  all  cases  the  lubricant  is 
fed  to  the  bearings.  Use  good  graphite,  hard  oil,  or  grease 
in  all  compression  cups,  and  screw  the  caps  down  so  as  to 
force  the  grease  through  the  journal  box.  When  the  machine 


32 


Fig.  19 


§34 


CONCRETE  WORK 


33 


is  in  operation,  a  turn  should  be  given  on  all  compression  cups 
at  least  once  every  2  hours. 

3b.  Instructions  for  Starting  and  Managing 
Boilers. — See  that  all  connections  with  the  boiler  are 
properly  made  and  are  tight.  Fill  the  boiler  up  to  or  above 
the  second  gauge  with  water,  and  take  particular  notice  while 
it  is  being  filled  that  all  handhole  plates  and  connections 
around  it  are  tight;  particularly  note  that  the  check-valve 
does  not  leak.  Build  a  slow  fire  in  the  boiler  until  the  water 
becomes  hot;  under  no  circumstances  force  the  fire  until  after 
steam  begins  to  generate;  this  can  be  determined  by  leaving 


Fig  20 


the  top  gauge-cock  open  until  steam  appears.  After  about 
10  or  15  pounds  of  steam  has  been  raised,  note  whether  there 
are  any  slight  leaks  appearing  in  the  boiler  or  its  connections. 
After  steam  has  been  raised  to  the  pressure  to  be  carried,  try 
the  safety  valve  and  be  sure  that  it  is  in  good  working  order. 
It  is  advisable  to  lift  the  safety  valve  from  its  seat  at  least 
twice  a  day.  Always  carry  the  water  in  the  boiler  at  a  height 
that  will  best  allow  the  engine  to  operate  without  carrying 
over  water  with  the  steam.  It  is  always  best  to  carry  the 
water-line  in  the  boiler  as  high  as  possible.  Never  allow 
the  fire-door  of  the  boiler  to  be  opened  except  when  firing 


34 


FIELD  OPERATIONS  AND 


§34 


the  boiler.  In  checking  steam,  always  close  the  ash-pit  doors 
and  damper  in  the  stack;  if  this  is  not  sufficient  to  check  the 
steam,  the  fire  should  be  banked.  When  shutting  the  boiler 
down  at  night,  under  no  circumstances  allow  the  fire-door 
to  remain  open. 

37.  Starting  and  Operating  tlie  Mixer. — In  starting 
the  mixer,  turn  the  machine  over  light  a  few  times,  meanwhile 
setting  up  such  runways  as  may  be  required.  See  that  the 
discharge  chute  is  in  position,  as  shown  by  the  dotted  lines 
at  a,  Fig.  20.  Feed  into  the  machine  the  amount  of  water 
required  for  the  batch.  Follow  with  stone,  sand,  and  cement 
in  the  order  named.  Let  the  material  remain  in  the  machine 
about  one-half  minute,  which  is  long  enough  under  average 
conditions,  and  then  reverse  the  chute  to  position  shown  at  b. 
Then  discharge  direct  into  wheelbarrows,  buckets,  or  other 
vehicles,  the  whole  batch  or  part,  as  desired.  Reverse  the 
chute  and  feed  into  the  machine  the  next  batch. 

In  securing  results  as  to  output,  watch  the  delivery  side  of 
the  machine;  get  all  the  material  out  at  once,  so  that  the  next 
batch  can  be  mixing.  If  it  is  necessary  to  discharge  only  part 
at  a  time,  use  the  largest  cart  or  barrow  that  can  be  obtained. 

An  occasional  inspection  of  the  journal-boxes  will  guard 
against  undue  wear,  which  may  result  in  bottoming  the 
main  gears,  with  disastrous  results  to  both  pinion  and  spur. 
Also  watch  that  the  rollers  do  not  wear  down  so  as  to  cause 
bottoming. 

DEVICES  TO  HANDLE  CONCRETE 


HAULING  DEVICES 

38.  Concrete  Carts. — In  large  work,  specially  con¬ 
structed  sheet-metal  carts  are  generally  used  to  convey 
the  concrete  from  the  discharge  end  of  the  mixer  to  the  place 
where  it  is  to  be  put  in  the  forms.  Such  a  cart  should  hold 
the  quantity  of  concrete  that  one  man  is  capable  of  wheeling, 
and  must  be  of  a  form  that  can  be  dumped  rapidly  and 
placed  for  dumping  with  some  degree  of  accuracy. 


I 


§34 


CONCRETE  WORK 


35 


A  concrete  cart  of  this  kind  is  illustrated  in  Fig.  21.  The 
wheels  of  this  cart  are  made  up  of  round-iron  spokes  and  a  flat 
bar  rim.  The  body  is 
made  of  tank  steel  with 
heavy  bar-iron  handles 
and  is  reinforced  by  ex¬ 
tensions  of  the  flat  bar- 
iron  handles  that  are 
bolted  to  its  sides.  The 
cart  is  very  convenient 
for  dumping  the  con¬ 
crete,  either  upon  the 
floor  or  into  the  forms 
in  a  wall  or  a  pit  con¬ 
struction. 

In  Fig.  22  the  cart  is  shown  entirely  inverted,  a  position  that 
it  assumes  when  the  concrete  is  dumped  upon  the  forms  of 
the  floor  construction.  When  it  is  required  to  dump  the 
concrete  into  wall  forms  or  pits,  the  handles  are  reversed  and 
the  cart  assumes  the  position  shown  in  Fig.  23. 

39.  Charging  Barrows. — A  type  of  barrow  used  to 
charge  the  mixer  is  illustrated  in  Fig.  24.  It  is  mounted  upon 
two  small  iron  wheels.  The  barrows  are  made  in  three  sizes, 

to  hold  3,  4,  or  5  cubic 
feet,  and  weigh  from 
145  to  160  pounds. 
The  barrow  is  of  a 
convenient  shape  for 
delivering  materials 
to  batch  mixers  ; 
and,  besides,  it  is 
dumped  by  tipping 
forwards,  instead  of 
sidewise,  as  with  the 
Fig.  22  ordinary  type  of 

wheelbarrow.  The  material  is  discharged,  without  spreading,  in 
a  straight  line  from  the  mouth  of  the  barrow.  As  shown  at  a 

211—17 


36 


FIELD  OPERATIONS  AND 


§34 


in  the  figure,  a  prong,  or  spur,  is  riveted  on  the  barrow  at  each 
side.  These  spurs  are  arranged  to  engage  in  sprocket  chains 


running  on  an  inclined  plane, 
necessary,  the  barrow  may 
be  wheeled  up  by  machinery. 


Therefore,  if  an  incline  is 


Fig.  24 


By  arranging  the  charging  platform  of  a  mixer  in  this  manner, 
the  barrow  with  its  load  is  rapidly  carried  up  the  incline, 
allowing  the  work  to  be  conducted  with  more  rapidity. 


Fig.  25 


40.  Wheelbarrows. — The  wheelbarrows  to  be  used  on 
reinforced-concrete  work  must  be  strongly  built,  those  con¬ 
structed  with  a  steel  tray  being  superior  to  the  ordinary 


§34 


CONCRETE  WORK 


37 


wooden  barrow.  Two  types  of  wheelbarrow,  known  as  the 
tray  mortar  barrow,  are  shown  in  Figs.  25  and  2G.  These 
barrows  are  provided  with  an  iron  wheel,  a  tray  of  stamped 
sheet  steel,  wooden  handles,  and  heavy  angle-iron  supporting 
legs.  Such  barrows  are  of  great  service  in  reinforced-concrete 


Fig.  26 


-work,  and  may  be  dumped  clean.  The  capacity  of  the  barrow 
shown  in  Fig.  25  is  about  44  cubic  feet,  and  that  of  the  one 
shown  in  Fig.  2G,  4  cubic  feet.  Both  are  suitable  for  dumping 
forwards  or  sidewise.  Wooden  extensions  to  the  handles  are 
carried  beyond  the  front  edge  of  the  tray. 


nOISTING  DEVICES 

41 .  Charging  Hoppers. — In  conjunction  with  concrete 
batch  mixers,  such  as  those  of  the  Ransome  type,  it  is  some¬ 
times  convenient  to  use  a  charging  hopper  of  the  type 
shown  at  a,  Fig.  27.  This  device  consists  of  a  sheet-steel 
trough,  into  which  the  material  from  charging  barrows  may 
be  dumped.  After  the  proper  number  of  barrow  loads  have 
been  dumped  into  the  hopper,  it  is  hoisted  up  and  the  material 
discharged  into  the  mixer.  In  the  Ransome  device,  the 
hopper  is  hoisted  by  means  of  a  small  friction  drum  mounted 
on  an  extension  to  the  engine  shaft.  With  such  a  device  the 
mixer  can  be  charged  in  20  seconds.  This  period  covers  the 
time  required  to  hoist  the  materials  and  to  lower  the  hopper 
to  the  ground  in  position  for  the  next  batch.  This  charging 
hopper  can  be  detached  from  the  batch  mixer  by  removing 
a  few  bolts. 


ffiTim 


I 


38 


Fig.  27 


§34 


CONCRETE  WORK 


39 


42.  Selecting  tlie  Method  of  Hoisting. — The 
principal  items  of  cost  in  reinforced-concrete  work  are  the 
transferring  of  the  materials  from  the  cars  to  the  bins  and 
thence  to  the  mixer,  and  the  handling  of  the  mixed  concrete 
from  the  discharge  hopper  of  the  mixer  to  the  points  where 
it  is  to  be  placed.  Usually,  the  concrete  is  mixed  on  the 
ground  near  the  site  of  the  operation,  though  sometimes  the 
mixing  plant  is  placed  upon  scaffolding  at  a  point  high  above 
the  structure.  In  this  case,  the  ingredients  are  hoisted  to 
the  platform  and  the  mixed  concrete  is  delivered  by  chutes 
or  other  means  to  the  points  where  it  is  to  be  deposited. 
In  all  instances,  the 
superintendent  or  fore¬ 
man  of  the  job,  provided 
it  comes  within  his  pro¬ 
vince,  should  determine 
the  most  economical 
method  of  handling  for 
the  particular  work  to 
be  done. 

43.  E  levator. 

For  hoisting  the  con¬ 
crete  to  the  platform 
of  concrete  mixers,  an 
ordinary  builders’ 
elevator  is  frequently 
employed.  This  elevator  is  made  sufficiently  large  to  carry 
one  or  two  wheelbarrows,  and  is  sometimes  arranged  so  that 
the  “empties”  are  coming  down  on  one  side  while  the  wheel¬ 
barrows  filled  with  the  concrete  are  going  up  on  the  other. 
On  large  jobs,  however,  it  is  advisable  to  use  hoisting  buckets 
of  large  capacity. 

44.  15ooni  Derrick. — For  work  of  moderate  size,  a 
boom  derrick  operated  by  a  hoisting  engine  and  erected  on 
some  adjacent  high  building  or  on  a  scaffolding  will  be  of 
great  value.  The  boom  should  be  long  enough  to  reach  over 
the  forms  and  the  sides  of  the  structure,  and  the  derrick  should 


Fig.  28 


Fig.  29 


40 


CONCRETE  WORK 


41 


§31 

be  fitted  with  either  an  ordinary  bucket  or  one  of  the  clam¬ 
shell  type.  It  can  be  used  to  deliver  the  ingredients  to  the 
mixer  and  the  concrete  from  the  mixer  to  the  forms. 

45.  Hoisting  Buckets  and  Bucket  Hoists. — In 

Fig.  28  is  shown  a  type  of  lioisting  bucket  arranged  to 
slide  up  and  down  on  guides  located  in  framework,  as  shown 
in  Fig.  29,  and  to  dump  automatically.  The  bucket  dumps 
where  the  front  guide  upon  which  the  edge  a,  Fig.  28,  rests 
is  stopped  off.  The  bucket  is  constructed  so  that  when  filled 
it  leans  against  the  guide.  Thus,  when  the  front  guide  ends, 
the  bucket  automatic¬ 
ally  dumps  forwards 
and  assumes  the  posi¬ 
tion  shown  dotted  at 
/,  Fig.  29.  The  bucket 
also  rights  itself  auto¬ 
matically  on  being 
lowered  after  dump¬ 
ing.  A  particular 
feature  of  this  bucket 
is  that  the  bottom  is 
formed  so  that  the 
bucket  scours  clean 
in  dumping. 

46.  The  bucket 
hoist  shown  in  Fig.  29  is  about  the  simplest  that  can 
be  devised  to  deliver  mixed  concrete  to  the  floor  levels 
of  a  building  under  construction,  and  will  be  found  con¬ 
venient  to  hoist  the  materials  to  an  elevated  concrete 
mixer.  The  framework  of  this  hoist  is  well  braced,  as 
shown.  Inside  of  the  framework  are  wooden  guides  a  for  the 
automatic  hoisting  bucket  b.  Hoisting  is  done  by  means  of 
a  friction  hoist  c,  which  winds  a  steel  rope,  or  cable,  over  the 
sheave  d  at  the  top.  The  friction  hoist  is  operated  through 
a  series  of  gears  by  means  of  a  link  belt  or  chain  running  upon 
a  sprocket  wheel  on  the  extension  to  the  shaft  that  operates 
the  mixer.  As  will  be  observed,  the  guide  e  is  stopped  off 


Fig.  31 


42 


§34 


CONCRETE  WORK 


43 


near  the  top.  Thus,  when  the  bucket  is  hoisted  to  the  posi¬ 
tion  shown  at  /,  owing  to  its  shape  and  the  fact  that  the 
center  of  gravity  of  the  contents  is  not  over  the  main  guides, 
it  automatically  tilts  and  assumes  the  position  shown  dotted. 
In  this  way,  the  concrete  is  discharged  into  the  concrete 
bin  g,  which  may  be  constructed  of  either  steel  Or  wood 
and  may  be  readily  closed  or  opened  by  the  Ransome  gate 
shown  in  detail  in  Fig.  30.  When  the  material  has  been 
delivered  to  the  hopper,  the  concrete  carts  in  the  building  can 
be  filled  and  the  material  conveyed  .to  the  particular  point 
where  it  is  to  be  placed.  At  h  is  shown  a  concrete  cart  in 
position,  ready  to  receive  the  concrete  mixture. 


COMBINED  HOISTING  AND  MIXfNG  DEVICES 

47.  In  the  construction  of  large  concrete  retaining  walls 
near  railroads,  a  device  similar  to  that  shown  in  Fig.  31  may 
be  successfully  used.  The  device  shown  in  the  figure  was 
employed  in  constructing  a  large  retaining  wall  at  the  Grand 
Central  Station  of  the  New  York  Central  Railroad  in  New 
York  City.  In  this  instance,  the  plant  consisted  of  a  concrete 
mixer  a  mounted  in  a  tower,  and  a  hoist  b  to  carry  up  the 
sand,  gravel,  and  broken  stone.  The  entire  tower  was 
mounted  on  railroad  car  wheels,  so  as  to  run  on  rails  placed 
13  feet  2  inches  apart.  The  platform  carrying  the  mixer  was 
supported  upon  a  braced  frame,  so  that  the  clear  distance 
above  the  rail  was  13  feet,  allowing  the  trains  to  pass  under 
the  tower.  Above  the  mixer  was  a  large  hopper  for  the  sand 
and  stone.  This  hopper  received  the  material  from  the  top 
of  the  tower,  and  from  it  the  material  was  deposited,  through 
chutes,  into  the  mixer.  The  stone  and  sand  were  delivered 
at  the  bottom  of  the  tower,  being  shoveled  from  cars  on  the 
adjacent  track  into  the  hoisting  buckets.  The  cement  was 
also  hoisted  in  one  of  these  buckets.  The  mixer  used  in  this 
instance  had  a  capacity  of  40  feet  of  loose  material  made  up 
of  4  cubic  feet  of  cement,  12  cubic  feet  of  sand,  and  24  cubic 
feet  of  stone.  The  rail  under  the  part  in  which  the  mixer 
was  located  was  5  feet  from  the  face  of  the  retaining  wall. 


44 


FIELD  OPERATIONS  AND 


§34 


It  may  be  interesting  to  know  that  in  conjunction  with  this 
work  a  locomotive  crane  was  used  to  advantage  in  lifting  and 
arranging  the  wall  forms,  which  were  constructed  in  panels. 
The  concrete  was  delivered  from  the  mixer  into  dumping  cars. 


Fig.  32 


These  cars  were  of  the  end-dump  pattern  and  traveled  on 
light  tracks  of  2-foot  gauge  erected  on  the  crosspieces  that 
connected  the  uprights  of  the  forms.  It  was  thus  possible  to 
deliver  the  concrete  to  any  part  of  the  forms  in  an  easy 
manner.  In  using  this  device,  250  cubic  yards  were  mixed 


§34 


CONCRETE  WORK 


45 


at  a  total  cost  of  $105,  making  the  cost  of  1  cubic  yard, 
including  the  mixing,  placing,  and  handling  of  the  ingredients, 
40  cents. 

48.  In  Fig.  32  is  shown  a  device  that  can  be  employed  to 
advantage  where  large  quantities  of  concrete  are  to  be  placed. 
As  shown  in  the  figure,  two  bucket  elevators  a  and  b  are 
arranged  to  convey  sand  and  broken  stone,  respectively,  to 
the  bins  /  and  g,  located  abt>ve  the  mixer  h.  The  materials 
are  delivered  to  the  plant  by  dump  wagons  e ,  which  run  on 
channel-iron  tracks,  and  are  dumped  into  the  hoppers  already 
mentioned.  The  cement  is  conveyed  to  the  mixer  by  an 
ordinary  dumping-bucket  hoist,  as  shown  at  i.  After  the 
materials  pass  through  the  mixer,  they  fall  into  the  hopper  /, 
from  which  the  mixed  concrete  may  be  conveyed  to  the  point 
of  deposit  by  means  of  carts  or  chutes. 

49.  Another  type  of  concrete  handling  and  mixing  plant 
that  was  used  successfully  in  the  construction  of  a  thirty-span 
viaduct  is  illustrated  in  Fig.  33.  As  shown  at  i,  this  plant 
has  the  usual  tower  construction  with  the  automatic  dumping 
bucket,  but  the  device  for  conveying  the  ingredients  to  the 
mixer  from  the  hopper  b  is  different  from  those  already 
described  The  device  used  here  is  known  as  a  skip,  and 
consists  of  a  small  open-front  car  that  is  drawn  up  the  incline 
by  means  of  a  rope  e  running  to  the  winding  drum  /.  On  the 
incline  are  two  tracks,  one  a  narrow  gauge  and  the  other  a 
wide  gauge,  built  on  the  same  center  line.  The  two  rear 
wheels  of  the  car  run  on  the  broad-gauge  rails,  while  the  front 
wheels  run  on  the  narrow-gauge  rails,  similar  to  the  device 
described  in  Art.  24.  In  assuming  the  dumping  position 
shown  at  a,  the  car  runs  forwards  with  its  front  wheels  on  the 
narrow-gauge  rails,  which  are  bent  down  to  the  horizontal 
position  shown  at  d.  The  hind  wheels,  however,  continue  on 
the  wide  gauge,  but  are  stopped  by  the  ends  of  the  track, 
which  are  bent  upwards.  After  the  car  is  emptied,  the  clutch 
on  the  winding  drum  is  released  and  the  car  is  pulled  back  to  its 
position  under  the  hopper,  as  at  g,  by  means  of  the  counter¬ 
weight  h. 


ww 


CC 

cc 

6 

(Z 


46 


§34 


CONCRETE  WORK 


47 


TOOLS  USED  IN  PLACING  CONCRETE 

50.  Tamping  Tools. — The  concrete  most  frequently  used 
in  reinforced-concrete  construction  is  a  wet  mixture.  For 


Fig.  34 


tamping  wet  mixtures,  the  slice  bar,  or  spade,  shown  in 
Fig.  34  is  generally  used.  This  bar  consists  of  a  plate  of  sheet 
steel  riveted  to  a  round-iron  bar  handle. 

With  a  bar  of  this  character,  the  concrete  can 
be  tamped  so  as  to  remove  all  the  air,  or 
voids,  from  it.  By  flat  spading  along  the 
sides  of  the  forms,  that  is,  by  pounding  on 
top  along  the  forms  with  the  back  of  the 
spade,  the  broken  stone  can  be  jarred  away 
from  the  form  boards  and  a  smooth  finish  of 
sand  and  cement  produced. 

51.  In  some  instances,  a  slice  bar  with 
perforations  in  the  blade  is  employed  for 
tamping.  When  flat  spading  with  a  perfor¬ 
ated  slice  bar,  the  liquid  cement  or  mortar 
is  allowed  to  run  through  the  holes  and  pass 
down  along  the  sides  of  the  forms. 

Other  types  of  rammers,  or  tamping  bars, 
are  shown  in  Figs.  35  and  3(3.  The  one  shown 
in  Fig.  35  is  used  for  natural  cement  mixtures, 
and  is  suitable  for  tamping  the  concrete  in 
small  places.  The  one  shown  in  Fig.  36  is 
commonly  used  for  tamping  such  work  as  con¬ 
crete  basement  or  cement  floors,  city  pave¬ 
ments,  and  other  flat  surfaces. 

52.  Concrete  Rollers. —  Cast-iron  or 
Fig.  35  sheet-steel  hand  rollers  are  frequently  em-  FlG>  36 

ployed  in  the  construction  of  concrete  floors  or  pavements. 
By  some’  engineers  rolling  is  considered  to  be  better  and 


48 


FIELD  OPERATIONS  AND 


§34 

cheaper  than  tamping.  However,  a  roller  is  not  always  advan¬ 
tageous  to  use  on  reinforced  concrete  floors,  for  frequently  the 
tamping  is  depended  on  to  bring  the  reinforcing  bars  or  rods 
up  from  the  centering.  By  tamping,  .the  jar  forces  the  con¬ 
crete  under  the  steel  and  thus  raises  it  to  its  proper  position. 
This  method  is  quite  frequently  employed  for  reinforced-con- 
crete  work,  and  the  same  results  could  not  be  accomplished 
by  the  roller. 

53.  A  type  of  roller  particularly  suitable  for  sidewalks 
and  the  concrete  base  of  cement  pavements  or  floors  is  illus¬ 
trated  in  Fig.  37.  This  roller  consists  of  a  cylinder  of  sheet 
steel  fitted  with  a  wrought-iron  shaft  extended  fo  receive  the 
handle  bars.  Such  rollers  are  made  30  inches  in  diameter 
and  about  36  inches  wide,  and  in  three  weights.  The  light 


Fig.  37 


roller  weighs  about  300  pounds;  the  medium,  375  pounds; 
and  the  heavy,  645  pounds.  In  using  the  rollers,  the  light 
roller  is  first  run  over  the  concrete ;  this  is  frequently  followed 
by  the  medium  roller  and  then  by  the  heavy  one.  However, 
the  light  roller  could  be  used  throughout  the  operation  by 
hanging  on  it  weights  properly  arranged  to  make  up  the 
weight  for  the  medium  and  the  heavy  roller. 


MACHINERY  FOR  BENDING  STEED 

54.  Bar-Twisting  Machine. — Reinforced-concrete 
contractors,  architects,  or  engineers,  in  putting  up  a  building 
are  seldom  called  on  to  twist  the  square  reinforcing  bars ;  how¬ 
ever,  with  large  operations,  the  steel  is  sometimes  twisted  at 
the  site.  For  such  a  purpose  a  bar- twisting  machine,  such 


§34 


CONCRETE  WORK 


49 


as  that  shown  in  Fig.  38,  is  sometimes  employed.  This 
machine  consists  of  a  fast  and  a  loose  pulley,  as  at  a,  carrying 
a  spur  pinion  that  engages  with  the  gear  operating  a  square 
chuck,  as  at  b,  into  which  the  bar  fits.  The  other  end  of  the  bar 
is  held  rigid  in  a  stationary  vise  device.  When  the  machine  is 
started,  the  steel  is  readily  twisted.  With  these  machines  are 
furnished  nine  sets  of  dies,  varying  from  £  to  1J  inches, 
inclusive,  the  sizes  advancing  by  J  inches.  Different  sets  of 
gears  are  also  furnished,  so  that  the  machine  can  be  run  at  the 
speed  required  for  the 
different-sized  bars. 

A  machine  of  this 
kind  requires  about 
12  horsepower.  It 
would  be  used  only 
on  a  very  extensive 
operation,  and  only 
then  after  the  con¬ 
tractor  has  found 
that  he  can  twist  the 
steel  at  less  cost  than 
he  can  buy  it  already 
twisted. 


55.  Tools  for 
Bending  Rods. 

On  all  large  rein- 
forced-concrete  jobs,  Fig.  38 

it  is  necessary  to  bend  a  great  number  of  the  steel  reinforcing 
bars  or  rods.  Especially  is  this  true  if  reinforced  floors  are  to 
be  constructed  and  if  some  of  the  reinforcing  rods  or  bars  are 
to  be  used  in  the  form  of  a  truss  in  order  to  take  care  of  the 
negative  bending  moments  in  the  beams  and  girders.  The 
smaller  rods  or  bars  are  easily  bent,  but  }-,  -J-,  1-inch,  and 
larger  bars  are  difficult  to  bend,  especially  if  the  bend  is  to 
be  short. 

In  Fig.  39  is  shown  a  device  that  may  be  used  conveniently 
for  bending  steel  rods  or  bars  of  the  usual  size  used  in  rein- 


50 


FIELD  OPERATIONS  AND 


§34 


forced-concrete  work.  It  consists  of  a  rigid  table,  or  bench,  a, 
upon  which  is  securely  bolted  a  cast-iron  vise  arrangement 
consisting  of  a  bedplate  b  that  has  pivoted  upon  it  two  cams, 
or  clamping  devices,  c.  These  cams  are  arranged  eccentric¬ 
ally  upon  a  pivot,  and  are  provided  with  a  handle  so  that  they 
can  be  turned  and  thus  clamp  a  straightedge  d  against 
the  steel  bar  to  be  bent.  The  bar  is  thus  held  between 
the  straightedge  and  the  flange  on  the  cast-iron  plate.  The 
figure  shows  the  bar  in  position  ready  for  bending.  The  bar 
after  bending  is  indicated  by  the  dotted  outline. 


Fig.  39 


56.  Numerous  other  devices  employed  by  the  contractor 
to  bend  steel  reinforcement  are  improvised  affairs  that  depend 
for  their  efficiency  on  the  ingenuity  of  the  superintendent  or 
foreman  designing  them.  If  the  bar  is  of  considerable  size, 
it  is  liable  to  bend  in  a  long,  easy  bend  instead  of  all  at  one 
point  as  desired.  When  this  occurs,  a  pipe  is  slipped  over  the 
bar  to  stiffen  it  so  that  it  can  be  bent  exactly  at  the  point 
where  it  leaves  the  vise.  A  piece  of  pipe  is  also  used  to 
increase  the  leaverage  when  a  short  end  of  a  bar  is  to  be  bent. 


§34 


CONCRETE  WORK 


51 


If  a  number  of  loops,  ties,  or  stirrups  are  to  be  bent,  it  is 
best  to  have  the  work  done  at  the  factory.  The  machines 
at  the  factory  will  bend  a  J-inch  bar  or  rod  and  turn  it  off 
in  a  loop  on  the  end  with  great  facility.  This  class  of  rein¬ 
forcement  can  therefore  be  bent  cheaper  away  from  the 
operation  than  it  can  on  the  site. 


NOTES  FOR  THE  SUPERINTENDENT 


PRECAUTIONS  TO  BE  OBSERVED 


CENTERING 

57.  The  various  methods  of  constructing  forms  and  notes 
regarding  them  are  contained  in  Form  Work.  There  are, 
however,  a  number  of  precautionary  measures  regarding  both 
form  work  and  concrete  work  that  the  superintendent  should 
be  familiar  with  and  that  he  should  bear  in  mind  continually. 

58.  Construction  of  Forms. — In  the  construction  of 
forms,  observe  that  the  forms,  or  centering,  are  built  according 
to  the  drawings  and  details  and  that  the  steel  is  properly 
placed  in  these  forms,  so  that  the  amount  of  steel  required 
by  the  plans  or  schedules  is  sure  to  be  included  in  the  concrete 
work  when  finished.  Observe  that  the  supports  of  the  forms 
are  well  braced  and  sufficiently  strong  to  carry  the  dead  load 
of  the  wet  concrete.  Many  failures  have  been  caused  by 
weakness  of  the  supports  for  concrete  centering.  Observe 
that  the  forms  do  not  shake  or  vibrate,  as  any  motion  destroys 
the  proper  set  of  the  concrete.  The  superintendent  should 
also  observe  that  the  forms  are  so  placed  and  so  supported 
from  the  ground  where  the  uprights  rest  upon  the  earth  as 
to  prevent  warping,  twisting,  or  sagging;  also,  that  forms  are 
entirely  clean  and  that  proper  openings  are  made  in  them  for 
cleaning  out  the  foot  of  columns. 

211—18 


52 


FIELD  OPERATIONS  AND 


§34 


59.  Filling  tlie  Forms. — In  filling  the  forms  with 
concrete,  it  should  be  observed  that  the  concrete  is  placed  in 
the  proper  quantities  at  one  time;  that  is,  that  the  slab  is 
filled  at  the  same  time  as  the  beams,  and  that  if  it  is  necessary 
to  stop  off  the  work,  good  judgment  is  exercised  regarding 
the  position  at  which  such  a  stop-off  is  made,  so  that  the 
structural  strength  of  the  finished  concrete  will  not  be 
destroyed. 

60.  Stripping  tlie  Forms. — In  no  instance  should  the 
centering  be  removed  until  it  has  been  conclusively  deter¬ 
mined  that  the  concrete  has  properly  dried  and  possesses 
sufficient  strength  to  carry  its  own  weight  and  any  weight 
that  may  be  placed  on  it  during  the  course  of  erection. 
Extraordinary  precautions  should  be  taken  where  it  is  known, 
that  freezing  weather  occurred  during  the  placing  of  the 
concrete.  Cubes  of  concrete  should  be  made  at  the  same 

t 

time  as  the  floor  construction.  These  should  be  examined 
later  and  tested,  if  necessary,  to  determine  whether  the 
concrete  has  the  proper  strength.  Even  when  the  forms 
have  been  removed,  it  is  better  to  leave  some  supports 
beneath  the  soffits  of  beams  and  girders,  leaving  where 
possible,  the  bottom  form  boards  in  place  for  another  week 
or  two  after  the  side  forms  have  been  stripped. 


WORKING  UNDER  UNFAVORABLE  CONDITIONS 

61.  Work  in  Freezing  and  Wet  Weather. — No  con¬ 
crete  should  be  laid  in  weather  under  33°  F.,  and  whenever 
possible  reports  from  the  Weather  Bureau  should  be  obtained, 
to  find  out  whether  or  not  a  cold  wave  is  expected.  If  such  a 
drop  in  temperature  is  looked  for,  it  is  better  to  suspend  work 
than  to  run  the  chances  of  a  severe  drop  in  the  temperature 
just  after  the  concrete  has  been  deposited.  Where  possible, 
stoves,  or  salamanders ,  are  used  on  the  floor  below  to  prevent 
the  freezing  of  the  work  above. 

In  wet  weather,  no  concrete  should  be  left  exposed  at  night, 
but  should  be  covered  with  salt  hay,  or  straw;  or,  better  still, 


§34 


CONCRETE  WORK 


53 


boards  should  be  placed  over  it,  with  a  space  beneath  that 
may  be  closed  in  with  canvas  on  the  sides  and  filled  with  straw 
or  hay. 

02.  Protection  of  Concrete  From  Rapid  Drying. 

In  warm  weather  or  weather  in  which  the  concrete  is  likely 
to  be  deprived  of  its  moisture  by  rapid  evaporation,  the 
concrete  should  be  wet  down  at  least  twice  a  day.  This  can 
be  done  by  sprinkling  or  by  covering  the  concrete  with  wet 
sand  or  straw. 

03.  Niglit  AVork. — The  placing  of  reinforced-concrete 
work  at  night  is  fraught  with  considerable  danger  and  should 
be  avoided  whenever  possible.  When  such  work  as  this 
comes  under  the  charge  of  the  superintendent,  he  must 
depend  on  the  illumination  available  and  take  every  pre¬ 
caution  to  safeguard  against  the  misplacing  of  steel  in  the 
forms  and  the  danger  of  fire  from  the  .lights. 


FINISH  OF  CONCRETE 

64.  Brush  Finish. — Concrete  surfaces  may  be  finished 
in  various  ways.  The  plastic  appearance  of  the  concrete  as 
it  comes  from  the  forms  has  always  been  objectionable,  and 
this  pasty,  or  plastic,  appearance  can  never  be  reconciled 
with  good  artistic  finish  or  effect. 

About  the  best  but  perhaps  the  most  difficult  method  of 
finishing  reinforced-concrete  surfaces  is  to  remove  the  forms 
from  the  concrete  about  12  hours  after  it  has  been  placed  and 
then  brush  the  surface  with  either  a  steel  brush  or  a  stiff 
rattan  brush.  By  this  means  the  cement  mortar  is  removed 
from  around  the  broken  stone  and  the  broken  stone  embedded 
in  the  mortar  is  exposed.  The  appearance  of  the  finish 
depends  on  the  broken  stone  used. 

A  very  excellent  finish  can  be  obtained  if  broken  trap  rock 
or  other  dark  stone  of  irregular  form  is  used  in  the  concrete. 
This  finish  is  shown  in  Figs.  40  and  41.  The  difference 
between  these  two  illustrations  is  simply  in  the  size  of  broken 
stone  used,  the  stone  shown  in  Fig.  40  being  larger  than  that 


* 


Pig.  40 


54 


oo 


Fig.  41 


56 


FIELD  OPERATIONS  AND 


§34 


in  Fig.  41.  The  variation  in  the  size  of  the  stone  employed, 
as  can  be  seen,  changes  materially  the  appearance  of  the 

surface. 

If  concrete  is  allowed 
to  set  more  than  12 
hours,  so  that  it  is  too 
hard  to  brush  by  the 
ordinary  method,  hy¬ 
drochloric  acid  and  water  must  be  used.  The  acid  softens 
the  mortar  so  that  it  can  be  brushed  in  the  ordinary  manner. 


65.  Hand  Work. — Besides  being  brushed,  or  washed, 
concrete  may  be  dressed  with  either  a  bush  or  a  patent 
hammer,  in  the  same  manner  as  stonework.  These  tools, 
however,  do  not  work  so  well  on  concrete  surfaces  as  they  do 
on  stone  surfaces,  because  the  concrete  is  not  so  uniform  in 
texture.  Special  forms  of  tools  have  therefore  been  devised 
for  the  finishing  of  concrete  work. 

66.  In  Fig.  42  is  shown  the  special  form  of  busli  hammer 
designed  to  dress  concrete.  The  points  on  the  face  of  this 
hammer  are  larger  and  farther  apart  than  are  the  points  on 
the  face  of  a  similar  hammer  adopted  for  stone  finishing. 
The  hammer  itself,  however,  is  about  the  same  size  as  a 
hammer  used  on  stone. 

In  Fig.  43  is  shown  an  ax  used  for  dressing  concrete  sur¬ 
faces.  This  ax  consists  of  a  wooden  handle  and  a  cast-steel 
head,  to  which  are  bolted  steel  blades.  As  the  blades  are 


Fig.  43 

removable,  sharp  blades  can  be  easily  substituted  for  dull 
ones.  The  dull  blades  can  be  sharpened  with  either  a  file  or 


57 


Fig.  44 


Fig.  45 


58 


CONCRETE  WORK 


59 


§34 


an  emery  wheel.  A  laborer  can  conveniently  dress  about 
100  square  feet  of  surface  a  day  with  this  type  of  ax,  so 
that  the  cost  is  from  I  V  to  2  cents  per  square  foot,  based  on 
a  10-hour  day. 

The  effect  of  dressing  concrete  with  either  the  special  bush 
hammer  or  the  special  ax  is  about  the  same.  In  either  case, 
it  is  most  pleasing.  The  finish  obtained  is  shown  in  Fig.  44. 

67.  Finishing;  With  Pneumatic  Hammers. — For 

finishing  large  surfaces  of  concrete  buildings  and  structures, 
a  pneumatic  hammer  or  tool  is  sometimes  used.  By  this 
means,  a  very  uniform  finish  is  produced,  as  shown  in  Fig.  45. 
This  finish  is  an  excellent  one  for  buildings  in  which  the 
concrete  work  has  various  architectural  features,  such  as 
cornices,  mutules,  corbels,  etc.  A  bush  hammer  is  used  on 
the  intricate  portions  of  the  work,  and  the  panels  and  other 
plane  portions  are  dressed  with  a  pneumatic  hammer. 

68.  Sand  Blast  Finish. — The  sand  blast  is  some¬ 
times  employed  for  finishing  concrete  surfaces.  It  removes 
the  plastic,  or  pasty,  effect  given  to  the  concrete  by  the  forms 
and  produces  a  granulated  finish,  somewhat  similar  to  sand¬ 
stone,  but  not  so  uniform,  because  the  aggregates  are  likely 
to  be  brought  out  irregularly.  Owing  to  the  cost  of  the 
equipment  for  a  sand  blast  and  the  indifferent  effect  that  is 
produced,  it  is  not  much  used. 


* 

. 


INTRODUCTION 


FIEIjD  inspection 

1.  The  hydraulic  cement  used  in  construction  work  is  of 
three  kinds,  namely,  Portland ,  natural ,  and  puzzolan ,  or 
cement.  In  reinforced-concrete  construction,  however,  and, 
in  fact,  in  all  important  structural  work,  Portland  cement  is 
employed  almost  exclusively  on  account  of  both  its  greater 
strength  and  its  greater  uniformity  and  reliability.  Natural 
cement  is  used  occasionally  in  repair  work  or  in  damp  or  wet 
places  where  its  property  of  quick  setting  is  advantageous, 
but  in  structural  work,  the  quantity  thus  employed  is  almost 
negligible.  The  greater  part  of  this  Section  will  therefore 
be  devoted  to  Portland  cement,  and  it  should  be  borne  in 
mind  that  when  the  unqualified  term  cement  is  used,  Portla?id 
cement  alone  is  to  be  understood. 

2.  Condition  and  Weight  of  Cement  Packages. 
In  order  to  determine  correctly  the  structural  value  of  a  ship¬ 
ment  of  cement,  an  examination  in  the  field  is  very  necessary. 
Portland  cement  is  packed  either  in  canvas  or  paper  bags  or 
in  wooden  barrels,  which  should  weigh  not  less  than  94  and 
376  pounds,  respectively.  A  number  of  packages  of  cement 
should  be  weighed  at  intervals,  and  the  average  weight 
should  never  be  permitted  to  fall  below  the  stipulated 
amount;  for,  since  mortar  and  concrete  are  usually  propor¬ 
tioned  on  the  assumption  of  this  weight,  the  resulting  mortar 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS  HALL,  LONDON 


g  35 


2 


TESTS  ON  CEMENT 


§35 


or  concrete  will  be  considerably  weaker  than  intended.  Each 
package  should  also  be  plainly  marked  with  the  brand  and 
name  of  the  manufacturer;  those  not  branded  should  be  dis¬ 
carded,  and,  if  possible,  a  mixture  of  different  brands  should 
be  avoided. 

3.  Condition  and  Color  of  Cement  in  Packages. 
A  possible  indication  of  inferiority  is  the  presence  of  lumps 
throughout  the  bulk  of  the  material.  On  standing,  cement 
gradually  absorbs  moisture  from  the  air.  At  first  this  mois- 
ture  is  present  in  merely  a  minute  and  harmless  state,  but 
eventually  it  combines  chemically  with  the  cement;  that  is, 
in  the  same  manner  as  when  cement  and  water  are  actually 
mixed  together  in  practice.  In  the  first  condition,  lumps 
usually  appear,  but  they  are  so  soft  that  they  may  be  readily 
crushed  with  the  fingers,  and  of  course  would  be  entirely 
broken  up  when  mixed  into  mortar.  When,  however,  the 
cement  contains  lumps  that  are  hard  and  pebble-like  and  that 
can  only  be  crushed  with  considerable  effort,  it  indicates 
that  chemical  action  has  begun.  Cement  containing  any 
appreciable  amount  of  these  hardened  lumps  is  generally  of 
decidedly  inferior  quality,  and  it  should  never  be  permitted 
to  enter  any  important  part  of  a  structure. 

For  reasons  to  be  explained  later,  seasoning  for  a  short 
length  of  time  is  beneficial  for  cement;  but  on  the  other 
hand,  storing  too  long  will  tend  to  weaken  it.  Cement 
from  2  to  6  months  old  is  usually  the  safest  and  will  pro¬ 
duce  the  best  results. 

4.  The  color  of  Portland  cement,  ranging  from  bluish  to 
yellowish  gray,  affords  no  indication  of  quality  except  in 
cases  where  different  shipments  or  different  parts  of  the 
same  shipment  show  a  variation  in  color,  thus  pointing  to  a 
lack  of  uniformity.  When  this  occurs,  tests  of  each  grade 
of  the  material  should  be  made  in  order  to  ascertain  whether 
all  of  it  is  good  quality  or  a  mixture  of  good  and  bad. 

Complete  field  inspection  thus  covers  an  examination  of 
the  condition  and  weight  of  the  packages,  and  of  the  condi¬ 
tion  and  color  of  their  contents. 


TESTS  ON  CEMENT 


3 


SAMPLING 

5.  Procuring  tlie  Sample. — In  securing  a  sample  for 
testing,  the  essential  point  is  to  get  one  that  will  fairly 
represent  the  entire  shipment  whose  qualities  are  to  be 
determined.  The  common  practice  is  to  take  a  small  por¬ 
tion  of  material  from  every  tenth  barrel,  or,  what  is  the  same 
thing,  from  every  fortieth  bag.  Thus,  in  a  carload  ship¬ 
ment  of  six  hundred  bags,  fifteen  bags  should  be  opened  and 
sampled.  When  tests  are  to  be  made,  however,  on  a  ship¬ 
ment  of  only  a  few  barrels,  more  packages  than  one  in  ten 
should  be  opened;  and  when  the  shipment  is  large,  say  over 
one  hundred  and  fifty  barrels,  it  should  be  subdivided  and 
each  portion  tested  separately.  The  bags  selected  should  be 
taken  at  random  and  from  different  layers,  and  not  all  from 

one  part  of  the  pile. 

The  cement,  moreover,  should  be  taken 
not  only  from  the  top  of  the  packages,  but 
from  the  center  and  sides  as  well.  When  the 
cement  is  contained  in  barrels,  a  sampling 
auger,  as  shown  in  Fig.  1,  is  used  to  extract 
the  sample,  a  hole  being  bored  in  the  staves 
midway  between  the  heads. 

(>.  Care  of  Sample. — After  the  samples 
of  cement  have  been  taken  from  the  packages 
they  are  thoroughly  mixed  in  a  can  or  basin, 
and  this  mixed  sample  is  used  for  the  various 
tests.  To  make  a  complete  series  of  tests, 
the  sample  should  contain  from  6  to  8  pounds. 
The  cement,  after  sampling  and  before  test- 
ing,  must  be  well  protected,  as  exposure  to 
heat,  cold,  dampness,  or  any  other  abnormal 
condition  may  seriously  affect  the  results.  Undoubtedly, 
many  errors  in  cement  testing  are  due  to  careless  handling 
of  the  samples. 


4 


TESTS  ON  CEMENT 


§35 


TESTS  OF  CEMENT 


PRELIMINARY  CONSIDERATIONS 

7.  Purpose  of  Testing. — In  order  that  a  mortar  or  a 
concrete  made  with  cement  shall  give  good  results  in  actual 
construction,  it  must  possess  two  important  properties, 
namely,  strength  and  durability.  The  resulting-  concrete 
must  be  sufficiently  strong  to  bear  any  reasonable  load 
imposed  on  it,  and  besides  must  be  able  to  withstand  suc¬ 
cessfully  the  forces  of  age,  weathering,  chemical  action,  or 
any  other  condition  that  will  tend  to  destroy  its  permanency 
or  impair  its  strength.  The  primary  purpose  of  cement 
testing,  therefore,  is  to  determine  whether  any  particular 
shipment  of  cement  possesses  sufficient  strength  and  dura¬ 
bility  to  admit  of  its  use  in  construction. 

8.  Classification  of  Tests. — A  determination  of  the 
quality  of  cement  necessitates  the  employment  of  several 
tests,  which  may  be  classified  as  primary  tests  and  secondary 
tests.  The  former  tests,  which  include  tests  for  sou?idness 
and  tensile  strength ,  are  made  to  give  directly  a  measure  of 
the  essential  qualities  of  strength  and  durability.  Unfor¬ 
tunately,  neither  of  these  tests  is  capable  of  being  made 
with  precision,  chiefly  because  each  experimenter,  no  matter 
how  careful  he  may  be,  handles  the  material  and  conducts 
the  experiment  in  a  slightly  different  manner.  Therefore, 
the  secondary  tests,  which  include  tests  to  determine  the 
time  of  setting,  the  fineness ,  the  specific  gi'avity,  and  the  chem¬ 
ical  analysis ,  are  made  to  obtain  additional  information  in 
regard  to  the  character  of  the  material.  However,  with  the 
possible  exception  of  the  test  of  time  of  setting,  the  second¬ 
ary  tests  have  but  little  primary  importance  and  indicate 
by  their  results  only  indirectly  the  properties  of  the  material. 


§35 


TESTS  ON  CEMENT 


5 


For  example,  it  has  been  proved  that  a  finely  ground  cement 
is  more  permanent  and  develops  greater  strength  than  one 
that  is  coarsely  ground;  but,  otherwise,  the  actual  size  of  the 
particles  is  immaterial.  Other  special  tests,  such  as  those 
for  compressive  and  transverse  strength ,  for  shear ,  abrasion , 
absorption,  porosity,  etc.,  are  made  occasionally  for  special 
reasons  or  for  research  work,  but  they  do  not  constitute  a 
part  of  the  ordinary  routine  of  cement  testing,  and  will 
therefore  not  be  considered. 

9.  Difficulties  of  Testing. — The  reason  why  tests  of 
cement,  and  especially  the  primary  tests,  are  so  difficult  and 
admit  of  so  many  possible  errors  is  that  they  are  not  made 
on  the  material  as  it  is  produced,  but  on  specimens  first  made 
in  the  laboratory,  and  in  which  the  material  is  radically 
changed  from  its  original  condition.  Bars  of  iron  and  wood, 
bricks,  and  such  materials  are  tested  in  the  form  in  which 
they  are  manufactured  and  used,  but  cement  is  made  as  a 
powder,  tested  mostly  as  a  paste,  and  used  as  a  mortar  or 
concrete.  The  specimens  for  testing,  moreover,  cannot 
advantageously  be  made  by  mechanical  means,  so  that  the 
different  style  of  handling  of  the  operator,  or  the  personal 
equation,  as  it  is  called,  becomes  an  important  factor. 

Accurate  cement  testing,  therefore,  is  largely  dependent 
on  the  knowledge,  care,  and  experience  of  the  operator,  for 
an  inexperienced  man,  no  matter  how  careful  and  conscien¬ 
tious  he  may  be,  can  never  be  relied  on  to  obtain  trustworthy 
results. 


PRIMARY  TESTS 


SOUNDNESS 

10.  Soundness  may  be  defined  as  the  property  of 
cement  that  tends  to  withstand  any  forces  that  may  operate 
to  destroy  or  disintegrate  it.  This  property  of  soundness, 
or,  as  it  is  sometimes  called,  constancy  of  volume,  is  the  most 
important  requisite  of  a  good  cement.  Although  the  original 
strength  of  the  material  may  have  been  sufficient,  if  it  is 


6 


TESTS  ON  CEMENT 


§35 

unsound  and  will  eventually  disintegrate,  it  is  both  worthless 
and  dangerous  for  purposes  of  construction. 

11.  Causes  of  Unsoundness. — The  most  common 
cause  of  unsoundness  in  Portland  cement  is  an  excess  of  free 
or  uncombined  lime,  which  crystallizes  with  great  increase 
of  volume,  and  thus  breaks  up  and  destroys  the  bond  of  the 
cement.  This  excess  of  lime  may  be  due  to  incorrect  pro¬ 
portioning  or  to  insufficient  grinding  of  the  raw  materials, 
to  underburning,  or  to  lack  of  sufficient  storing  before  use, 
called  seasoning.  A  certain  amount  of  seasoning  is  usually 
necessary,  because  almost  every  cement,  no  matter  how  well 
proportioned  or  burned  it  may  be,  will  contain  a  small  amount 
of  this  excess  of  lime,  which,  on  standing,  will  absorb  mois¬ 
ture  from  the  air,  slake,  and  become  inert.  Thus,  it  fre¬ 
quently  happens  that  a  cement  failing  in  the  tests  for 
soundness  will  pass  these  tests  easily  after  the  expiration  of 
a  few  weeks. 

Excess  of  magnesia  or  the  alkalies  may  also  cause  unsound¬ 
ness,  but  the  ordinary  cement  rarely  contains  a  sufficient 
amount  of  these  ingredients  to  be  harmful.  Sulphate  of 
lime  is  occasionally  responsible  for  unsoundness,  but  this 
ingredient  usually  acts  in  the  opposite  direction,  tending  to 
make  sound  a  cement  that  otherwise  might  disintegrate. 

12.  Methods  of  Determining  Soundness. — Although 
the  presence  of  free  or  loosely  combined  lime  is  recognized 
as  the  most  potent  factor  in  producing  unsoundness,  and 
although  this  lime  is  a  more  or  less  well-defined  chemical 
ingredient,  it  nevertheless  is  impossible  to  tell  by  any  known 
method  of  chemical  analysis  what  proportion  of  the  total 
lime  present  exists  in  this  dangerous  condition.  Therefore, 
physical  tests  must  be  relied  on  exclusively  for  the  detection 
of  unsoundness. 

The  property  of  soundness  is  determined  in  one  or  more 
of  three  ways:  by  measjirements  of  expansion,  by  normal  tests , 
and  by  accelerated  tests. 

13.  Measurements  of  expansion  are  made  by  forming 
specimens  of  cement,  usually  in  the  shape  of  prisms,  and 


§35 


TESTS  ON  CEMENT 


7 


measuring  the  change  in  volume  by  means  of  a  micrometer 
screw.  A  crude  form  of  this  test,  once  in  common  use,  con¬ 
sisted  in  filling  a  lamp  chimney  with  cement  paste  and  putting 
it  away  until  the  cement  became  hard.  If  the  expansion  of 
the  paste  in  hardening  caused  the  chimney  to  crack,  the 
cement  was  considered  to  have  failed  in  the  test.  At  the 
present  time,  however,  it  is  believed  that  expansion  is  not  a 
sure  index  of  unsoundness,  so  that  these  tests  are  seldom 
employed. 

14.  Normal  tests  consist  in  making  specimens  of 
cement  mixed  with  water,  preserving  them  in  air  or  in  water 
under  normal  conditions,  and  observing  their  behavior.  The 
common  practice  is  to  make  from  a  paste  of  neat,  or  pure, 
cement  two  circular  pats,  about  3  inches  in  diameter,  i  inch 
thick  at  the  center,  and  tapering  to  a  thin  edge,  on  glass 
plates  about  4  inches  square.  These  pats  are  kept  in  moist 
air  for  24  hours;  then  one  of  them  is  placed  in  fresh  water  of 
ordinary  temperature  and  the  other  is  preserved  in  air.  The 
condition  of  the  pats  is  observed  7  days  and  28  days  from 
the  date  of  making,  and  thereafter  at  such  times  as  may 
be  desired. 

15.  The  most  characteristic  forms  of  failure  are  illus¬ 
trated  in  the  following  figures,  which  must  be  carefully 


studied  by  any  one  desiring  to  make  tests,  for,  while  some 
of  the  cracks  indicate  unsoundness  and  poor  material,  others 

211—19 


8 


TESTS  ON  CEMENT 


§35 


Fig.  4 


Fig.  5 


Fig.  6 


Fig.  7 


Fig.  8 


§35 


9 


TESTS  ON  CEMENT 

show  conditions  that  are  entirely  harmless.  Many  cements 
of  excellent  quality  have  been  condemned  through  improper 
interpretation  of  the  normal  pat  tests. 

Fig.  2  shows  a  pat  in  good  condition. 

Fig.  3  illustrates  shrinkage  cracks  that  are  due,  not  to 
inferior  cement,  but  to  the  fact  that  the  pat  has  been  allowed 
to  dry  out  too  quickly  after  being  made.  Pats  must  be  kept 
in  a  moist  atmosphere  while  hardening,  or  these  cracks, 
indicative  merely  of  careless  manipulation,  will  develop. 

Fig.  4  shows  cracks  that  are  due  to  the  expansion  of  the 
cement.  This  condition  is  common  in  the  air  pats,  and  is 
not  indicative  of  injurious  properties.  Pats  kept  in  water, 
however,  should  not  show  these  cracks. 

Fig.  5  shows  three  pats  that,  for  different  reasons,  have 
left  the  glass  plate  on  which  they  were  made.  The  disk 
shown  in  (a)  left  the  plate  because  of  lack  of  adhesion; 
the  one  in  (b),  through  contraction;  and  the  one  in  (r), 
through  expansion.  The  condition  illustrated  in  {a)  is 
never  dangerous  in  either  air  or  water;  that  in  ( c )  is  only 
dangerous  when  existing  in  a  marked  degree;  and  that  in  ( b ) 
hardly  ever  occurs  in  water  but  in  air  it  often  indicates 
dangerous  properties.  Air  pats  that  develop  the  curvature 
shown  in  ( b )  generally  disintegrate  later.  A  curvature  of 
about  f  inch  in  a  3-inch  pat  can  be  considered  to  be  about 
the  limit  of  safety. 

Fig.  6  shows  cracking  of  the  glass  plate  to  which  the  pat 
is  attached.  This  cracking  is  caused  by  expansion  or  con¬ 
traction  of  the  cement,  combined  with  strong  adhesion  to  the 
glass.  It  rarely  indicates  injurious  properties. 

Fig.  7  illustrates  blotching  of  the  pats,  the  cause  of  which 
should  always  be  investigated  by  chemical  analysis  or  other¬ 
wise,  which  may  or  may  not  warrant  the  rejection  of  the 
material.  Slag  cements  or  cements  adulterated  with  slag 
invariably  show  this  blotching. 

Fig.  8  shows  the  radial  cracks  that  mark  the  first  stages 
of  disintegration.  Such  cracks  should  never  occur  with 
good  material.  They  are  signs  of  real  failure,  and  cement 
showing  them  should  never  be  used. 


10 


TESTS  ON  CEMENT 


§35 


In  Fig.  9  are  shown  illustrations  made  from  photographs 
that  illustrate  the  complete  failure  of  normal  pats.  The  two 
pats  in  (a)  and  ( b )  were  kept  underwater  during  the  testing 
period.  In  these  pats,  cracks  similar  to  those  shown  in 
Fig.  8  have  developed.  Of  the  air-dried  samples,  shown 


Fig.  9 


in  (c)  and  (d),  the  first  shows  failure  by  crumbling  and 
the  other  by  excessive  concavity.  The  concavity  of  the 
surface  is  shown  by  the  shadow  thrown  by  the  rubber 
band  that  surrounds  the  pat.  A  similar  pat  is  shown  in 
Fig.  5  (b). 


§35 


TESTS  ON  CEMENT 


11 


1G.  The  normal  pat  tests  are  the  only  absolutely  fair 
and  accurate  methods  of  testing  cements  for  soundness,  but 
the  serious  objection  to  them  lies  in  the  fact  that  frequently 
several  months  or  even  years  elapse  before  failure  in  the 
cement  so  tested  becomes  apparent.  To  overcome  this 
difficulty,  the  accelerated  tests  have  been  devised.  These 
tests  aim  to  hasten  the  action  of  the  expansive  ingredients 


by  treating  the  cement  with  heat  or  chemical  salts,  so  that  if 
there  is  any  tendency  to  incipient  disintegration,  it  will  occur 
at  once.  They  are  intended  to  produce  in  a  few  hours 
results  that  require  months  in  the  normal  tests. 

Many  forms  of  accelerated  tests  have  been  devised,  among 
which  may  be  mentioned  exposure  to  hot  water,  boiling 


12 


TESTS  ON  CEMENT 


35 


water,  steam,  steam  under  pressure,  hot  air,  direct  flame, 
and  chemical  salts,  such  as  calcium  chloride.  At  present, 
however,  the  only  tests  employed  commercially  are  the 
boiling  test  and  the  steam  test. 

17.  The  boiling  test  is  made  by  forming  specimens  of 
neat-cement  paste  into  pats,  such  as  are  employed  for  the 
normal  tests,  or  preferably  into  balls  about  li  inches  in 
diameter.  The  specimens  are  allowed  to  remain  in  moist 
air  for  24  hours  and  are  then  tested. 

0 

The  form  of  apparatus  used  for  the  boiling  test  is  shown 
in  Fig.  10.  It  consists  of  a  copper  tank  that  is  heated  by  a 


Fig.  11 


Bunsen  burner  and  is  filled  with  water.  The  water  in  the 
tank  is  kept  at  a  uniform  height  by  means  of  a  constant- 
level  bottle.  A  wire  screen  placed  an  inch  from  the  bottom 
of  the  tank  prevents  the  specimens  from  coming  into  contact 
with  the  heated  bottom.  The  24-hour-old  test  pieces  are 
placed  in  the  apparatus,  which  is  filled  with  water  of  a  normal 
temperature,  and  heat  is  applied  at  a  rate  such  that  the  water 
will  come  to  boiling  in  about  i  hour.  Quiet  boiling  is  con¬ 
tinued  for  3  hours,  after  which  the  specimens  are  removed 
and  examined.  Care  must  be  taken  that  the  water  employed 
is  clean  and  fresh,  because  impure  water  may  seriously  affect 
the  results.  The  same  water,  also,  should  never  be  used  for 


§35 


TESTS  ON  CEMENT 


13 


more  than  one  test.  A  good  cement  will  not  be  affected  by 
this  treatment,  and  the  ball  will  remain  firm  and  hard. 
Inferior  cement  will  fail  by  checking,  cracking,  or  entirely 
disintegrating,  as  shown  by  the  specimens  illustrated  in 
Fig.  11. 

18.  The  steam  test  is  made  in  the  same  way  as  the 
boiling  test,  except  that  instead  of  immersing  the  specimens 
in  water,  they  are  kept  in  the  steam  above  the  water.  The 
apparatus  employed  is  the  same  as  that  used  for  the  boiling 
test.  The  wire  screen,  however,  is  raised  so  that  it  is  an 
inch  above  the  surface  of  the  water;  also,  there  must  be  pro¬ 
vided  a  cover  that  is  close  enough  to  retain  the  steam  with¬ 
out  creating  pressure.  The  steam  test  is  less  severe  than 
the  boiling  test,  is  somewhat  less  accurate,  and  is  used  but 
infrequently. 

A  combination  of  the  steam  and  boiling  tests  is  sometimes 
made  by  first  steaming  the  specimens  and  then  placing  them 
in  the  boiling  water,  but  this  process  has  little  to  recommend  it. 

19.  Results  of  Tests  for  Soundness. — The  results 
of  the  normal  tests,  if  properly  made  and  interpreted,  may 
be  considered  reliable  guides  to  the  soundness  of  the  material, 
and  cement  failing  in  these  tests  should  always  be  rejected. 
The  accelerated  tests,  on  the  other  hand,  furnish  merely 
indications,  and  are  by  no  means  infallible.  A  cement  pass¬ 
ing  the  boiling  test  can  generally  be  assumed  sound  and  safe 
for  use,  but,  if  failure  occurs,  it  simply  means  that  other 
tests  should  be  performed  with  greater  care  and  watch¬ 
fulness.  It  often  is  advisable  to  hold  for  a  few  weeks 
cement  that  fails  in  boiling,  so  that  the  expansive  elements 
may  have  an  opportunity  to  hydrate  and  become  inert;  but 
if  the  material  fulfils  all  the  conditions  except  the  boiling 
test,  and  is  sound  in  the  normal  tests  up  to  28  days,  it  is 
generally  safe  for  use.  All  things  being  equal,  however, 
a  cement  that  will  pass  the  boiling  test  is  to  be  preferred. 


14 


TESTS  ON  CEMENT 


35 


TENSILE  STRENGTH 

20.  The  tensile- strength  test  is  for  the  purpose  of, 
ascertaining  a  measure  of  the  ability  of  the  material  to  with¬ 
stand  the  loads  that  the  structure  must  carry.  This  test  is 
made  by  forming  specimens,  called  briquets ,  of  cement  and 
cement  mortar,  and  determining  the  force  necessary  to  rup¬ 
ture  them  in  tension  at  the  expiration  of  fixed  intervals  of 
time.  Cement  constructions  are  rarely  called  on  to  with¬ 
stand  tensile  stresses,  but  if  the  tensile  strength  is  known, 
the  resistance  to  other  forms  of  stress  may  be  computed 
with  a  fair  degree  of  accuracy.  The  tensile-strength  test  is 
the  most  convenient  for  laboratory  determinations,  on  account 
of  the  small  size  of  the  specimens  and  the  comparatively  low 
stress  required  to  cause  rupture. 

Cement  is  tested  both  neat,  or  pure,  and  in  a  mortar  com¬ 
monly  composed  of  1  part  of  cement  and  3  parts  of  sand. 
The  periods  at  which  the  briquets  are  broken  have  been 
fixed  by  usage  at  7  days  and  28  days  after  making,  although 
tests  covering  much  longer  periods  of  time  are  necessary  in 
research  or  in  investigative  work. 

21.  Normal  Consistency. — The  strength  of  cement 
and  cement  mortars  varies  considerably  with  the  amount  of 
water  employed  in  making  the  briquets.  Dry  mixtures  ordi¬ 
narily  give  the  higher  results  for  short-time  tests,  and  wet 
mixtures  show  stronger  with  a  greater  lapse  of  time.  For 
testing  purposes,  therefore,  it  is  essential  that  all  cements 
be  mixed,  not  with  the  same  amount  of  water,  but  with  the 
amount  that  will  bring  all  the  cements  to  the  same  physical 
condition,  or  to  what  is  called  normal  consistency.  Dif¬ 
ferent  cements  require  different  percentages  of  water  because 
of  their  varying  chemical  composition,  degree  of  burning, 
age,  fineness,  etc. 

The  normal  consistency  of  neat-cement  pastes  may  be 
determined  by  either  of  the  methods  that  follow.  In  these 
tests,  the  quantities  are  given  in  grams.  The  grain  is  the 
metric  unit  of  weight.  One  kilogram  =  1,000  grams  =  2.205 
pounds;  1  gram  =  15.432  grains. 


TESTS  ON  CEMENT 


15 


§35 

1.  In  the  first  method,  500  grams  of  cement  is  weighed 
and  placed  on  a  mixing  slab  in  the  form  of  a  crater,  and  a 
definite  amount  of  water  poured  into  the  center.  The  cement 
is  turned  over  from  the  sides  into  the  center  until  the  water  is 
absorbed.  It  is  then  kneaded  for  1  minute,  after  which  it 
is  placed  in  the  conical  rubber  ring  under  the  plunger  of  the 
Vicat  needle  (see  Fig.  17).  The  plunger  is  brought  into 
contact  with  the  surface  of  the  material,  quickly  released, 
and  its  penetration  noted.  The  penetration  should  be 
exactly  10  millimeters,  and  if  the  test  shows  a  greater  or 
less  amount,  other  trials  must  be  made,  using  more  or  less 
water,  until  the  correct  consistency  is  obtained. 

One  millimeter  is  toVo  meter,  the  unit  length  of  the  metric 
system;  1  inch  =  25.4  millimeters;  10  millimeters  =  1  centi¬ 
meter  =  .3937  inch. 

2.  A  simpler  method  is  to  form  of  the  paste  a  ball  about 
2  inches  in  diameter  and  to  drop  this  ball  on  a  table  from  a 
height  of  about  2  feet.  If  the  cement  is  of  the  correct  con¬ 
sistency,  the  ball  will  not  crack  nor  will  it  flatten  to  less  then 
half  its  original  thickness.  The  percentage  of  water  required 
will  vary  from  16  to  25,  depending  on  the  characteristics  of 
the  material,  the  average  cement  taking  about  20  per  cent. 

22.  Consistency  of  Sand  Mortars. — The  consistency 
of  sand  mortars,  however,  cannot  be  obtained  by  either  of 
the  foregoing  methods,  because  the  sand  grains  do  not 
permit  of  the  measurement  of  the  consistency  by  penetration, 
and  the  mixture  is  too  incoherent  for  use  of  the  ball  method. 
For  mortars,  therefore,  it  is  necessary  to  employ  a  formula 
by  means  of  which  the  sand  consistency  can  be  computed 
when  that  of  the  neat  paste  is  known.  Several  such  formulas 
have  been  devised,  of  which  the  following  is  adaptable  to 
the  greatest  variety  of  conditions. 

Let  x  =  per  cent,  of  water  required  for  sand  mixture; 

N  =  per  cent,  of  water  required  to  bring  neat  cement 
to  normal  consistency; 
n  —  parts  of  sand  to  one  of  cement; 

N  =  a  constant  depending  on  the  character  of  the  sand. 


16 


TESTS  ON  CEMENT 


§35 


Then, 


3iV+  Sn  +  1 
4  (n  +  1) 


For  crushed-quartz  sand,  the  constant  N  is  30;  for  Ottawa 
sand,  it  becomes  25;  and  for  the  bar  and  bank  sands  used  in 
construction,  it  varies  from  25  to  35,  and  must  be  determined 
for  each  particular  sand. 


Example. — How  much  water  is  required  in  a  mixture  of  1  part  of 
cement  and  3  parts  of  crushed-quartz  sand?  The  neat  cement  requires 
19  per  cent,  of  water  to  give  normal  consistency. 


Solution. — Here,  AT  =  19,  S'  =  30,  and  n  =  3.  Substituting  these 
values  in  the  formula, 


x 


3X19  +  30X3  +  1 
4  X  (3  +  1)  ' 


per  cent. 


Ans. 


EXAMPLES  FOR  PRACTICE 

1.  How  much  water  will  be  required  in  a  mixture  of  1  part  of 

cement  to  5  parts  of  Ottawa  sand,  provided  the  neat  cement  requires 
20  per  cent,  of  water?  Ans.  7.75  per  cent. 

2.  (a)  Find  the  value  of  S  if  a  mixture  of  1  part  of  cement 
(JV  =  19)  and  4  parts  of  a  bank  sand  requires  8.5  per  cent,  of  water. 
(5)  What  percentage  of  water  will  be  required  for  a  mixture  of  1  part 
of  another  cement  (./V  =  22)  and  2  parts  of  the  same  sand? 

Ans  P°)  -S'  =  28 

s ‘  1  (b)  10.3  per  cent. 


It  is  extremely  important  that  all  cements  have  the  correct 
consistency  when  tested,  for  if  the  briquets  are  either  too 
wet  or  too  dry,  the  results  will  be  in  considerable  error  and 
hence  valueless.  Also,  in  order  to  avoid  the  introduction  of 
possible  irregularities,  care  must  be  taken  that  the  water  is 
clean,  pure,  and  of  a  temperature  as  near  70°  F.  as  practicable. 

23.  Sand  for  Mortar  Tests. — The  size,  gradation,  and 
shape  of  the  particles  of  sand  with  which  cement  mortars  are 
made  have  great  influence  on  the  resulting  strength.  Thus, 
for  testing  purposes,  it  is  essential  that  the  size  and  char¬ 
acteristics  of  the  sand  be  uniform.  There  are  two  varieties 
of  standard  sand  for  cement  testing,  one  an  artificial  sand  of 
crushed  quartz,  the  particles  of  which  are  angular  in  shape, 


§35 


TESTS  ON  CEMENT 


17 


and  the  other  a  natural  sand  from  Ottawa,  Illinois,  the 
particles  of  which  are  almost  spherical.  Both  sands  are 
sifted  to  a  size  that  will  pass  a  sieve  of  20  meshes  to  the 
inch  and  be  retained  on  a  sieve  of  30  meshes,  the  diameters 
of  the  sieve  wires  being  .0165  and  .0112  inch,  respectively. 
The  Ottawa  sand  will  develop  strengths  in  1-3  mortars 
about  20  to  30  per  cent,  greater  than  those  obtained  with 
crushed  quartz,  and  it  is  theoretically  the  better  sand  for 
testing,  but,  at  present,  crushed  quartz  is  more  extensively 
employed.  On  most 
important  works, 
tests  for  purposes  of 
comparison  are  also 
made  of  the  actual 
sand  entering  the 
construction. 

24.  Form  of 

Briquet. — The  form 
of  tensile  briquet 
adopted  as  standard 
in  the  United  States 
is  shown  in  Fig.  12. 

Its  length  over  all  is 
3  inches,  and  its  cross- 
section  is  exactly 
1  square  inch.  This 
form  of  briquet  is  by 
no  means  perfect,  and 
often  fails  under  test 
through  stresses  that 

Fig.  12 

are  not  pure  tension. 

Although  its  defects  are  recognized,  it  will  probably  con¬ 
tinue  as  the  standard  for  some  time  to  come,  because  of  the 
difficulties  arising  from  any  change. 

25.  Molds. — Cement  briquets  are  made  in  molds  that 
come  either  single  or  in  gangs  of  three,  four,  or  five.  The 
gang  molds  are  preferable,  as  they  tend  to  produce  greater 


18 


TESTS  ON  CEMENT 


35 


uniformity  in  the  results.  A  common  type  of  a  four-gang 
mold  is  shown  in  Fig.  13.  Molds  should  be  made  of  brass  or 
of  some  other  non-corrodible  material;  those  made 
of  cast  iron  soon  rust  and  become  unfit  for  use. 


26.  Method  of  Making  Briquets. — Many 
methods  of  mixing  and  molding  briquets  are  used 
in  various  laboratories,  but  the  following  is  the 
one  most  generally  employed  and  the  only  one 
that  has  been  officially  adopted  by  the  technical 
societies: 

First,  1,000  grams  of  cement  is  carefully 
weighed  and  placed  on  the  mixing  table  in  the 
form  of  a  crater,  and  into  the  center  of  this  is 
poured  the  amount  of  water  that  has  previously 
been  determined  to  give  the  correct  normal  con¬ 
sistency.  Cement  from  the  sides  of  the  crater  is 
then  turned  into  the  center,  by  means  of  a  trowel, 
until  all  the  water  is  absorbed,  after  which  the  mass  is 
vigorously  worked  with  the  hands,  as  dough  is  kneaded, 
for  li  minutes.  When  sand  mixtures  are  being  tested, 
250  grams  of  cement  and  750  grams  of  sand  are  first 
weighed  and  thoroughly  mixed  dry  until  the  color  of  the 
pile  is  uniform;  then  the  water  is  added  and  the  operation  is 
completed  by  vigorous  kneading. 

After  kneading,  the  material  is  immediately  placed  in  the 
molds,  which  should  first  have  been  wiped  with  oil  to  pre¬ 
vent  the  cement  from  sticking  to  them.  The  entire  mold  is 
filled  with  material  at  once — not  compacted  in  layers — and 
pressed  in  firmly  with  the  fingers  without  any  ramming  or 
pounding.  An  excess  of  material  is  then  placed  on  the  mold 
and  a  trowel  drawn  over  it  under  moderate  pressure,  at  each 
stroke  cutting  off  more  and  more  of  the  excess  material, 
until  the  surface  of  the  briquets  is  smooth  and  even.  The 
mold  is  then  turned  over,  and  more  material  placed  in  it  and 
smoothed,  as  before.  The  mixing  and  molding  should  be 
performed  on  a  surface  of  slate,  glass,  or  some  other  smooth, 
non-absorbent  material.  During  the  mixing  the  operator 


§35 


TESTS  ON  CEMENT 


19 


should  wear  rubber  gloves,  so  as  to  protect  his  hands  from 
the  action  of  the  lime  in  the  cement. 

Many  attempts  have  been  made  to  devise  apparatus  for 
making  briquets  by  mechanical  means,  and  while  some  such 
machinery  is  on  the  market  and  produces  fairly  good  results, 
the  process  is  much  slower  and  no  more  accurate  than  the 
hands  of  an  experienced  operator. 

27.  Storage  of  Briquets. — For  24  hours  after  making, 
the  briquets  are  stored  in  a  damp  closet  so  that  the  cement 
can  harden  in  a  moist  atmosphere.  This  condition  is  con¬ 
ducive  to  the  greatest  uniformity,  and  also  prevents  the 
formation  of  shrinkage  cracks  in  the  material.  The  damp 
closet  is  simply  a  tight  box  of  soapstone  with  doors  of  wood 
lined  with  zinc,  or  some  similar  arrangement,  with  a  recep¬ 
tacle  for  water  at  the  bottom  and  racks  for  holding  the 
briquets.  Sometimes,  when  there  is  no  closet,  the  briquets 
are  covered  with  a  damp  cloth,  which  method  answers  the 
purpose  but  is  less  uniform  and  accurate.  If  a  cloth  is  used, 
it  should  be  kept  damp  by  immersing  the  ends  in  water,  and 
care  should  be  taken  that  the  cloth  does  not  come  into  actual 
contact  with  the  surface  of  the  briquets. 

28.  The  briquets  remain  in  the  molds  while  in  the  damp 
closet,  but  at  the  expiration  of  24  hours  they  are  removed, 
marked,  and  placed  in  water  until  broken.  Cement  briquets 
are  stored  in  water  rather  than  in  air,  because  they  are  thus 
kept  under  more  uniform  conditions,  and  also  because  the 
presence  of  injurious  elements  is  generally  manifested  more 
clearly  in  this  environment.  Any  suitable  receptacle  will 
serve  for  their  storage,  provided  care  is  taken  to  have  water 
that  is  clean,  fresh,  and  at  a  temperature  of  nearly  70°  F. 
If  provision  cannot  be  made  to  keep  the  water  slowly 
running,  it  must  be  changed  not  less  than  once  a  week, 
otherwise,  it  soon  becomes  strongly  alkaline  and  may  seri¬ 
ously  affect  the  results. 

29.  Testing  Machines. — The  many  machines  designed 
for  the  purpose  of  breaking  the  briquets  may  be  divided  into 
those  of  the  shot-machine  type  and  those  of  the  beam  type. 


20 


TESTS  ON  CEMENT 


35 


30.  A  typical  shot  machine  as  made  by  the  Fairbanks 
Company  is  shown  in  Fig.  14.  It  is  constructed  on  the  cast- 
iron  frame  a ,  and  is  operated  as  follows: 

The  cup  /  is  hung  on  the  end  of  the  beam  d ,  the  poise  r 
placed  at  the  zero  mark,  and  the  beam  balanced  by  turning 
the  weight  /.  The  hopper  b  is  then  filled  with  fine  shot,  and 
the  briquet  to  be  tested  is  placed  in  the  clips  h.  The  hand- 


Fig.  14 


wheel  p  is  now  tightened  sufficiently  to  cause  the  graduated 
beam  d  to  rise  to  the  stop  k,  and  the  automatic  valve  j 
opened  so  as  to  allow  the  shot  to  run  into  the  cup  /.  The 
flow  of  the  shot  can  be  regulated  by  means  of  a  small 
valve  located  where  the  spout  joins  the  reservoir.  When  the 
briquet  breaks,  the  beam  d  drops  and  by  means  of  the  lever  t 


§35 


TESTS  ON  CEMENT 


21 


automatically  closes  the  valve  j.  After  the  specimen  has 
broken,  the  cup  with  its  contents  is  removed,  and  the 
counterpoise  g  is  hung  in  its  place.  The  cup  /  is  then  hung 
on  the  hook  under  the  large  ball  e ,  and  the  shot  weighed. 
The  weighing  is  done  by  using  the  poise  r  on  the  graduated 
beam  d  and  the  weights  n  on  the  counterpoise  g.  The 
result  will  show  the  number  of  pounds  required  to  break  the 
specimen.  A  mold  for  a  single  briquet  is  shown  at  c. 

31.  The  Olsen  machine  shown  in  Fig.  15  is  an  example 
of  the  beam  type  of  testing  machine.  In  this  machine,  an 


electric  motor  a  operates,  through  a  belt  d ,  the  step  pulleys 
b  and  c ,  which  are  used  to  change  the  speed  of  operation. 
A  belt  (hidden  by  the  frame  of  the  machine)  from  the  step 
pulley  c  operates  the  shaft  e,  which,  through  the  friction 


22 


TESTS  ON  CEMENT 


§35 


wheel  /,  turns  a  long  screw  that  runs  behind  the  beam^  and 
is  hidden  by  it.  The  weight  h  is  threaded  on  this  screw,  the 
same  as  an  ordinary  nut  would  be  threaded  on  a  bolt,  and  as 
the  motor  runs,  it  revolves  the  screw  and  draws  the  weight 
out  on  the  beam  at  a  uniform  rate  of  speed.  This  rate  can 
be  changed,  if  desired,  by  shifting  the  belt  on  the  step  pulleys 
b  and  c.  The  briquet  to  be  tested  is  inserted  in  the  clips 
and  drawn  tight  by  the  hand  wheel  i.  The  weight  h  is  then 
run  to  the  zero  point  of  the  scale,  and  the  hand  wheel  j  is 
turned  until  the  pointer  k  floats;  that  is,  touches  the  frame  at 
neither  l  nor  m.  The  motor  is  now  started  and  the  weight  h 
moves  out  on  the  scale.  At  the  same  time  the  hand  wheel  j 
is  turned  by  hand,  so  as  to  keep  the  pointer  k  balanced,  or 
floating.  When  the  briquet  breaks,  the  motor  is  stopped 
immediately  by  an  electrical  contrivance  at  n  and  the  load  is 
read  off  the  scale  g.  The  hand  wheel  j  may  also  be  operated 
by  the  motor  through  a  worm-wheel,  but  it  is  better  operated 
by  hand,  as  the  operator  must  turn  it  only  enough  to  keep  the 
pointer  k  always  in  mid-position. 

There  are  several  other  machines  in  the  market  as  suit¬ 
able  for  the  purpose  as  those  selected  for  illustration,  but, 
although  differing  in  many  minor  particulars,  all  of  them  are 
practically  of  one  or  the  other  of  these  types. 

32.  Form  of  Clip. — The  standard  form  of  clip  for 
holding  the  briquet  is  shown  in  Fig.  16,  the  bearing  sur¬ 
faces  a  being  li  inches 
apart,  i  inch  wide,  and 
shaped  to  fit  the  curve  of 
the  sides  of  the  briquet. 
Clips  are  often  made  with 
roller  bearings,  adjustable 
plate  bearings,  cushioned 
bearings,  etc.,  but  the  results 
of  tests  made  on  these  clips 
are  not  comparable  with 
those  made  on  the  standard 
clip,  and  hence  their  use  should  not  be  permitted. 


§35 


TESTS  ON  CEMENT 


23 


33.  Rate  of  Loading. — The  load  should  be  applied  in 
all  tests  at  the  uniform  rate  of  600  pounds  per  minute. 
Variations  in  this  speed  will  affect  the  results  seriously, 
higher  values  being  obtained  when  the  rate  of  loading  is 
increased,  and  lower  ones  when  it  is  diminished.  The 
briquets  should  be  broken  as  soon  as  they  are  removed  from 
the  storage  tanks  and  while  they  are  still  wet,  because  dry¬ 
ing  out  tends  to  lower  their  strength.  The  average  of  from 
three  to  five  briquets  should  be  taken  as  the  result  of  a  test. 

34.  Results  of  Tensile-Strength.  Tests. — The  tensile 
strength  of  cement  tested  in  the  preceding  manner  should 
increase  with  age  up  to  about  3  months,  and  should  then 
remain  practically  stationary  for  longer  periods.  The 
average  results  of  tests  of  Portland  cement  made  in  the 
Philadelphia  laboratories,  covering  a  period  of  several  years 
and  based  on  over  200,000  briquets,  are  given  in  Table  I. 


TABLE  I 

TENSILE  STRENGTH  OF  CEMENT  BRIQUETS 

( Pounds  per  Square  Inch ) 


i 

Mixture 

1  Hour  in  Air 

23  Hours  in 
Water 

I 

1  Day  in  Air 

6  Days  in  Water 

_ 

i  Day  in  Air 

27  Days  in 
Water 

1  Day  in  Air 

89  Days  in 
Water 

Neat . 

420 

710 

770 

775 

i  cement,  i  crushed-quartz  sand 

360 

590 

695 

700 

i  cement,  2  crushed-quartz  sand 

2  10 

370 

455 

465 

1  cement,  3  crushed-quartz  sand 

105 

2  10 

300 

310 

1  cement,  4  crushed-quartz  sand 

60 

130 

210 

230 

1  cement,  5  crushed-quartz  sand 

35 

80 

155 

195 

Specifications  for  strength  commonly  stipulate  minimum 
values  for  the  7-  and  28-day  tests,  the  customary  require¬ 
ments  for  Portland  cement  being  500  pounds  at  7  days  and 


211—20 


24 


TESTS  ON  CEMENT 


35 


600  pounds  at  28  days,  when  tested  neat,  and  170  pounds  at 
7  days  and  240  pounds  at  28  days,  when  tested  in  a  mortar 
consisting-  of  1  part  of  cement  and  3  parts  of  crushed-quartz 
sand.  When  Ottawa  sand  is  used,  the  requirements  for 
mortar  should  be  raised  to  200  and  280  pounds,  respectively. 
Retrogression  in  strength  of  the  neat  briquets  between  7  and 
28  days  is  not  necessarily  indicative  of  undesirable  properties, 
but  if  the  mortar  briquets  show  retrogression,  the  cement 
should  be  condemned.  Abnormally  high  strength  in  the 
7-day  test  of  neat  cement,  say  over  900  pounds,  may  gener¬ 
ally  be  taken  as  an  indication  of  weakness  rather  than  of 
superiority,  because  such  a  condition  is  usually  created  by 
an  excess  of  lime  or  of  sulphates,  either  of  which  may 
be  injurious.  Neat  cement  testing  from  600  to  800  pounds 
at  7  days  is  generally  the  most  desirable. 


SECONDARY  TESTS 


TIME  OF  SETTING 

35.  Reasons  for  Test. — The  time-of-setting  test  is 
made  to  determine  whether  or  not  the  cement  will  become 
hard  at  the  time  most  desirable  in  actual  construction.  If  it 
begins  to  set  too  soon,  the  crystallization  of  the  particles 
will  have  begun  before  the  mortar  or  concrete  is  thoroughly 
tamped  into  place,  and  working  the  mixture  after  setting  has 
begun  tends  to  break  up  the  crystals  and  to  weaken  the 
product.  If,  on  the  other  hand,  the  cement  sets  too  slowly, 
the  material  is  more  likely  to  suffer  from  exposure  to  heat, 
cold,  dampness,  and  frost;  also,  the  progress  of  the  work 
will  be  much  delayed  on  account  of  the  greater  interval 
required  between  different  sections,  and  the  longer  time  the 
forms  must  be  left  up. 

36.  Cement  when  mixed  into  a  paste  with  water  and 
allowed  to  stand,  gradually  changes  from  a  plastic  state  into 
a  hardened  mass.  This  process  is  known  as  setting,  while 
the  subsequent  action  resulting  in  increased  tensile  strength 


§35 


TESTS  ON  CEMENT 


25 


is  known  as  hardening.  In  the  setting  of  cements,  two 
stages  are  recognized:  (1)  When  the  paste  begins  to  harden, 
or  to  offer  resistance  to  change  of  form,  called  initial  set, 
and  (2)  when  the  setting  is  complete,  or  when  the  mass 
cannot  be  appreciably  distorted  without  rupture,  called  hard 
set.  The  time-of-setting  test  consists,  therefore,  in  deter¬ 
mining  the  time  required  for  the  cement  to  reach  these  two 
critical  points. 

The  test  is  made  by  mixing  cement  with  the  amount  of 
water  required  to  produce  normal  consistency,  in  the  same 
manner  as  for  neat  tensile  briquets,  forming  specimens, 
placing  them  under  one  of  the  forms  of  apparatus,  and 
observing  the  time  that  elapses  between  the  moment  the 
mixing  water  is  added  and  the  moments  when  the  paste 
acquires  initial  set  and  hard  set. 


37.  Forms  of  Apparatus  for  Time-of-Setting  Test. 
There  are  two  forms  of  apparatus  employed  to  test  the  time 
of  setting,  namely,  the  Vicat 
needle  and  the  Gillmore  wires . 

The  former  is  the  more  accurate 
and  the  one  adopted  as  standard, 
although  the  Gillmore  wires  are 
used  extensively. 

38.  The  Vicat  needle, 
shown  in  Fig.  17,  consists  of  a 
frame  k ,  holding  a  movable 
rod  /,  which  carries  a  cap  d  at 
the  upper  end  and  a  needle  h 
at  the  lower.  A  screw  /  holds 
the  rod  in  any  desired  place. 

The  position  of  the  needle  is 
shown  by  a  pointer  moving 
over  a  graduated  scale.  The 
rod  with  needle  and  cap  weighs 
exactly  300  grains,  and  the 
needle  is  1  millimeter  in  diameter  with  the  end  cut  off  square. 
When  making  tests  of  normal  consistency  (see  Art.  21),  the 


26 


TESTS  ON  CEMENT 


§35 


plunger  b  is  substituted  for  the  needle  h ,  and  the  cap  a  for  the 
cap  dy  the  difference  in  weight  between  the  needle  and  plunger 
being  compensated  by  the  difference  in  the  weight  of  the 
caps.  The  mold  i  for  holding  the  cement  paste  is  in  the 
form  of  a  truncated  cone.  It  has  an  upper  diameter  of  6  centi¬ 
meters,  a  lower  diameter  of  7  centimeters,  and  a  height  of 
4  centimeters,  and  rests  on  a  4"  X  4"  X  glass  plate  j. 

After  the  cement  paste  is  mixed,  the  mold  is  filled  by 
forcing  the  cement  through  the  large  end;  then,  after  turning 
it  over  and  smoothing  the  top,  it  is  placed  on  the  glass  plate 
under  the  needle.  The  needle  is  lowered  until  it  is  exactly 
in  contact  with  the  surface  of  the  paste,  then  quickly  released, 
and  the  depth  to  which  it  penetrates  read  from  the  grad¬ 
uated  scale.  Initial  set  is  said  to  have  taken  place  when 
the  needle  ceases  to  penetrate  to  within  5  millimeters  of  the 
bottom  of  the  specimen;  and  hard  set  takes  place  when  the 
same  needle  ceases  to  make  an  impression  on  the  surface. 
Trials  of  penetration  are  made  every  5  or  10  minutes,  until 
these  points  are  reached. 

39.  The  Gillmore  wires,  shown  in  Fig.  18,  consist  of 


two  wires,  one  having  a  di¬ 
ameter  of  iV  inch  and  carry¬ 
ing  a  weight  of  i  pound  and 
the  other  having  a  diameter 
of  -2-4  inch  and  carrying  a 
weight  of  1  pound.  The 
cement  paste  is  molded  into 
any  form  having  a  smooth 
surface,  and  the  wires,  or 
needles ,  as  they  are  called, 
are  rested  upon  it  from  time 
to  time.  Initial  set  takes 


Fig.  18 


place  when  the  light  wire  ceases  to  penetrate  the  surface  of 
the  paste,  and  hard  set  occurs  when  the  heavy  wire  ceases  to 
penetrate.  Care  must  be  taken  to  apply  the  needles  in  a 
precisely  vertical  direction,  because  if  resting  at  an  angle, 
the  area  under  the  pressure  will  be  reduced  and  the  results 


§35 


TESTS  ON  CEMENT 


27 


increased  accordingly.  More  accurate  results  will  be  obtained 
if  the  wires  are  held  upright  in  a  special  frame  made  for 
this  purpose.  Tests  made  with  the  Gillmore  wires  give 
results  averaging  from  one  and  one-half  to  two  times  as 
great  as  those  determined  by  means  of  the  Vicat  needle. 

40.  Time  of  setting  varies  considerably  with  the  amount 
of  mixing  water  employed,  so  that  it  is  essential  that  every 
sample  tested  be  brought  exactly  to  normal  consistency; 
otherwise,  the  results  may  be  in  decided  error.  Variations 
in  temperature,  in  both  environment  and  in  the  mixing  water, 
also  influence  the  results.  Standard  practice  requires  that 
both  the  materials  and  the  room  in  which  the  tests  are  made 
be  at  a  temperature  of  as  nearly  70°  F.  as  practicable. 

41.  Results  of  Time-of-Setting  Tests. — In  specifying 
results  to  be  obtained  in  testing  the  time  of  setting,  it  is 
obvious  that  a  minimum  value  should  be  stipulated  for  initial 
set  and  a  maximum,  as  well  as  a  minimum,  for  hard  set. 
It  must  also  be  remembered  that  a  cement  mixed  with  an 
aggregate  and  with  an  excess  of  water  in  the  field,,  will 
require  from  two  to  four  times  as  long  to  set  as  the  neat- 
cement  paste  mixed  with  little  water  in  the  laboratory. 
Cement,  therefore,  showing  an  initial  set  at  the  expiration 
of  20  minutes  with  the  Vicat  needle,  will  rarely  begin  to  set 
on  the  actual  work  in  less  than  f  hour,  which  gives  ample 
time  for  mixing  and  placing  the  materials;  and  cement  setting 
in  less  than  10  hours,  will  usually  have  hardened  completely 
in  the  work  in  24  or,  at  least,  in  36  hours.  Specifications 
usually  stipulate  that  Portland  cement  shall  show  initial  set 
in  not  less  than  20  minutes,  and  shall  develop  hard  set  in  not 
less  than  1  hour  nor  more  than  10  hours.  Cement  reaching 
initial  set  in  less  than  12  or  15  minutes  should  never  be  used 
for  any  work. 


FINENESS 

42.  Reasons  for  Fineness  Test. — When  cement,  in 
the  process  of  manufacture,  leaves  the  rotary  kiln  after 
burning,  it  is  in  the  form  of  round  balls  of  clinker  about 


28 


TESTS  ON  CEMENT 


35 


the  size  of  a  walnut.  This  clinker  is  reduced  by  grinding 
to  a  powder,  and  the  object  of  the  fineness  test  is  to  deter¬ 
mine  the  degree  of  this  pulverization.  The  fineness  of 
cement  is  important,  because  it  affects  both  the  strength 
and  the  soundness  of  the  product.  The  more  finely  a  cement 
is  ground,  the  more  thoroughly  will  the  cement  paste  cover 
the  particles  of  sand;  hence,  the  greater  will  be  the  strength 
of  the  resulting  mixture.  Also,  because  the  fine  particles 
are  more  quickly  acted  on  by  the  mixing  water,  the  crystal¬ 
lization  is  hastened,  so  that  not  only  is  the  ultimate  strength 
of  the  product  increased,  but  the  hardening  also  is  more 
rapid.  The  strength  of  neat  cement  is  reduced  somewhat 
when  the  cement  is  ground  especially  fine,  but  this  is  of  little 
importance,  because  cement  is  rarely  used  neat;  and  when  it 
is  so  used,  strength  is  seldom  a  factor. 

Fineness  of  grinding  affects  the  soundness  of  cement 
because  the  expansive  elements  contained  in  the  coarse 
particles  are  not  readily  susceptible  to  the  action  of  season¬ 
ing,  which  will  hydrate  and  render  inert  the  unsound  material 
in  the  fine  particles.  As  a  rule,  it  will  be  found  that  only 
the  coarser  part  of  cement  is  instrumental  in  causing  failure 
in  the  soundness  tests,  as  may  easily  be  determined  by 
making  comparative  tests — one  by  boiling  the  cement  in  its 
original  condition,  and  another  by  boiling  a  sample  of  the 
same  cement  from  which  the  coarse  particles  have  been 
separated  by  sifting.  Another  effect  of  increased  fineness 
is  to  hasten  the  time  of  setting;  thus,  with  such  cement,  the 
set  test,  as  well  as  the  addition  of  plaster  used  to  retard 
the  set,  must  be  closely  watched. 

43.  Apparatus  for  Fineness  Test. — The  fineness  of 
cement  is  determined  by  passing  it  through  a  series  of  sieves 
of  different  mesh  and  then  measuring  the  amount  retained 
on  each.  Three  sieves  are  commonly  employed,  namely, 
those  having  50,  100,  and  200  wires  to  the  linear  inch,  or 
2,500,  10,000,  and  40,000  meshes  to  the  square  inch,  respect¬ 
ively.  The  sieves  are  generally  circular  in  shape,  6  to 
8  inches  in  diameter,  2  to  3  inches  deep,  and  have  the  wire 


§35 


TESTS  ON  CEMENT 


29 


cloth  mounted  2  inch  from  the  bottom.  A  cover  and  a  pan 
to  catch  the  material  passing  through  the  sieve  should  also 
be  provided. 

For  accurate  work,  it  is  necessary  that  the  wire  cloth  be 
regular  and  of  exactly  the  proper  mesh,  for,  because  of  the 
uniform  gradation  of  the  particles  of  cement,  the  least  vari¬ 
ation  in  the  mesh  of  the  sieves  becomes  noticeable  in  the 
results.  Sieves  for  cement  testing  should  never  be  used 
until  they  have  been  carefully  examined  and  found  to  conform 
to  the  following  standard  specifications: 

1.  Cloth  for  cement  sieves  shall  be  of  woven  brass  wire 
of  the  following  diameters:  No.  50,  .0090  inch;  No.  100, 
.0045  inch;  and  No.  200,  .00235  inch. 

2.  Mesh  to  count  on  any  part  of  the  sieve  as  follows: 
No.  50,  not  less  than  48  nor  more  than  50  per  linear  inch; 
No.  100,  not  less  than  96  nor  more  than  100  per  linear  inch;  and 
No.  200,  not  less  than  188  nor  more  than  200  per  linear  inch. 

3.  Cloth  to  be  mounted  squarely  and  to  show  no  irregu¬ 
larities  of  spacing. 

44.  Method  of  Making  the  Fineness  Test. — The 
method  of  using  the  sieves  in  the  fineness  test  is  to  weigh 


Fig.  19 


out  50  grams  of  cement  on  a  scale  sensible  at  least  to 
•To  gram  and  to  place  it  on  the  No.  200  sieve,  on  which  it  is 


30 


TESTS  ON  CEMENT 


35 


shaken  until  not  more  than  iV  gram  passes  the  sieve  at  the 
end  of  1  minute  of  shaking.  The  arrival  of  this  stage  of 
completion  can  be  watched  either  by  using  a  pan  under  the 
sieve  or  by  shaking  over  a  piece  of  paper.  The  residue 
remaining  on  the  sieve  is  weighed,  placed  on  the  No.  100 
sieve,  and  the  operation  repeated,  again  weighing  the 


Fig.  20 


\ 


residue.  The  amount  remaining  on  the  No.  50  sieve  is  then 
determined  similarly.  Scales  like  those  shown  in  Fig.  19 
are  convenient  for  this  test,  and  may  be  so  graduated  that 
either  the  percentage  of  residue  or  of  the  amount  passing 
each  sieve  may  be  read  directly  from  the  beam.  The  process 
of  sifting  can  be  accelerated  by  placing  a  small  quantity  of 
coarse  shot  or  pebbles  on  the  sieves  with  the  cement  during 


§35 


TESTS  ON  CEMENT 


31 


the  shaking.  These  may  be  separated  from  the  cement  by 
passing  the  residue  with  the  shot  through  a  coarse  sieve, 
such  as  the  No.  20. 

45.  Mechanical  sifters  like  that  illustrated  in  Fig.  20, 
manufactured  by  Howard  &  Morse,  of  Brooklyn,  New  York, 
may  be  used  in  the  fineness  test.  The  sieves  are  arranged 
in  nests,  the  finest  being  at  the  bottom,  and  the  coarsest 
sieve  at  the  top.  The  cement  to  be  tested  is  placed  on  the 
top  sieve.  Three  or  four  nests  may  be  placed  in  the  machine 
at  one  time,  and  after  turning  it  until  the  sifting  is  complete, 
the  amount  remaining  on  each  sieve  is  weighed.  For  deter¬ 
mining  the  granulometric  composition  of  sands  for  use  in 
mortar,  as  described  in  Sa?ids  a?id  Cements ,  this  machine  is 
particularly  well  adapted.  By  granulometric  composition  of 
sand  is  meant  the  percentage  of  the  different  sizes  of  grains 
contained  in  a  given  sample. 

46.  Results  of  Fineness  Tests. — Portland  cement 
should  be  ground  to  such  a  fineness  that  it  will  leave  a 
residue  of  not  more  than  25  per  cent.,  by  weight,  on  the 
No.  200  sieve,  and  not  more  than  8  per  cent,  on  the  No.  100 
sieve.  Of  these  two  requirements,  the  first  is  the  more 
important,  because  it  is  only  that  part  of  the  cement  passing 
the  finest  sieve  that  is  active  in  the  setting  and  hardening  of 
the  material.  The  amount  remaining  on  the  No.  100  sieve 
is  also  important,  because  this  part  is  most  liable  to  cause 
unsoundness  in  the  cement,  and  although  specifications  do 
not  call  for  tests  with  the  No.  50  sieve,  it  is  usually  employed 
for  the  same  reason  as  the  No.  100  sieve.  Any  appreciable 
residue  on  this  sieve  indicates  that  the  material  is  much  more 
liable  to  unsoundness.  Any  cement  failing  to  pass  the  fine¬ 
ness  test  should  be  watched  more  carefully  in  the  soundness 
and  strength  tests,  but  if  these  tests  show  good  results  up  to 
28  days,  the  cement  can  as  a  rule  be  used  safely.  It  must 
be  remembered,  however,  that  only  that  part  passing  the 
No.  200  sieve  is  really  cement,  so  that  a  coarsely  ground 
shipment  is  practically  equivalent  to  one  adulterated  with 
weak  and  unsound  material. 


32 


TESTS  ON  CEMENT 


§35 


SPECIFIC  GRAVITY 

47.  Reasons  for  Specific-Gravity  Test. — The  object 
of  the  specific-gravity  test  is  to  furnish  indications  of  the 
degree  of  burning,  the  presence  or  absence  of  adulteration, 
and  the  amount  of  seasoning  that  the  cement  has  received. 
When  Portland  cement  is  burned,  the  separate  ingredients 
are  in  close  contact  and  gradually  combine  by  a  process  of 
diffusion.  The  greater  the  amount  of  this  burning,  the  more 
thoroughly  are  the  elements  combined.  Thus,  by  their  con¬ 
traction  they  give,  in  volume,  a  higher  density  or  specific 
gravity.  Since,  to  secure  good  cement  the  burning  must 
have  been  made  within  definite  limits,  it  follows  that  the 
specific  gravity  must  also  lie  within  fixed  limits  if  the  cement 
has  been  properly  manufactured. 

The  common  adulterants  of  Portland  cement,  namely, 
limestone,  natural  cement,  sand,  slag,  cinders,  etc.,  all  have 
specific  gravities  ranging  from  2.6  to  2.75,  while  the  specific 
gravity  of  Portland  cement  averages  about  3.15.  An  appre¬ 
ciable  amount  of  adulteration,  therefore,  is  at  once  indicated 
in  the  results  of  the  test.  For  example,  suppose  a  cement 
whose  specific  gravity  is  3.15  is  adulterated  so  as  to  contain 
20  per  cent,  of  sand  whose  specific  gravity  is  2.65.  The 
specific  gravity  of  the  mixture  would  then  be  .80  X  3.15  +  .20 
X  2.65  =  3.05,  the  adulteration  thus  becoming  obvious. 

Seasoning  is  indicated  because  the  cement  on  standing 
gradually  absorbs  water  and  carbonic  acid  from  the  air. 
These  ultimately  combine  with  it  and  thus  lower  the  specific 
gravity.  The  amounts  of  water  and  carbonic  acid  combined 
and  absorbed  may  be  approximately  determined  by  making 
tests  of  the  specific  gravity  of  the  cement  in  its  original  con¬ 
dition,  on  another  sample  dried  at  212°  F.,  and  on  one 
ignited  over  a  blast  lamp.  The  difference  between  the  first 
two  tests  gives  a  measure  of  the  absorbed,  or  hygroscopic, 
water,  and  the  difference  between  the  last  two  gives  a 
measure  of  the  combined  water  and  carbonic  acid,  because 
igniting  the  cement  restores  it  more  or  less  to  the  condition 
of  the  original  clinker. 


35 


TESTS  ON  CEMENT 


33 


48.  Apparatus  for  Specific-Gravity  Test. — Of  the 
many  forms  of  apparatus  employed  for  the  specific-gravity 
test,  the  Le  Cliatelier  flask,  shown  in  Fig.  21,  is  the  one 
most  commonly  used.  It  is  also  the  one  adopted  by  the 
technical  societies  as  standard.  It  consists  of  a  glass  flask 
about  30  centimeters  high.  The  lower 
part  up  to  the  mark  a  contains  120  cubic 
centimeters,  and  the  bulb  between  the 
marks  a  and  b  contains  exactly  20  cubic 
centimeters.  The  neck  of  the  flask  above 
the  mark  b  is  graduated  into  tV  cubic 
centimeters.  The  funnel  c  inserted  in  the 
neck  is  to  facilitate  the  introduction  of 
the  cement. 


49.  Method  of  Making  the  Spe¬ 
cific-Gravity  Test. — The  specific 
gravity  of  a  substance  has  been  defined 
as  the  ratio  of  its  weight  to  the  weight 
of  an  equal  volume  of  water,  or,  when 
the  metric  system  of  weights  and  meas¬ 
ures  is  used,  the  ratio  of  its  weight,  in 
grams,  to  its  displaced  volume,  in  cubic 
centimeters.  The  method  of  conducting 
the  test  is  as  follows:  Sixty-four  grams 
of  cement  is  carefully  weighed  on  scales 
that  should  have  a  sensibility  of  at  least 
.005  gram.  The  flask,  Fig.  21,  is  filled 
to  the  lower  mark  a  with  benzine  or 
kerosene,  which  has  no  action  on  the 
cement,  and  carefully  adjusted  precisely 
to  the  mark  by  adding  the  liquid  a  drop  at  a  time.  The 
funnel  is  then  placed  in  the  neck  of  the  flask  and  the 
weighed  cement  introduced  slowly  through  it,  the  last 
traces  of  the  cement  being  brushed  through  with  a 
camel’s-hair  brush.  The  funnel  is  then  removed  and  the 
height  of  the  benzine  read  from  the  graduations,  esti¬ 
mating  to  .01  cubic  centimeter.  The  displaced  volume  is 


Fig.  21 


34 


TESTS  ON  CEMENT 


§35 


then  20  plus  the  reading  in  cubic  centimeters,  and  the  specific 
gravity  of  the  cement  is  64  divided  by  that  quantity.  For 
example,  suppose  that  the  reading  on  the  flask  is  .54,  then 
the  displaced  volume  will  be  20  +  .54  =  20.54  and  the 
specific  gravity  will  be  64  -r-  20.54  =  3.116. 

The  apparatus  must  be  protected  from  changes  in  temper¬ 
ature  while  in  use,  because  even  touching  the  flask  with  the 
fingers  will  change  the  volume  of  the  liquid  noticeably.  The 
flask  is  sometimes  immersed  in  water  during  the  tests,  to 
prevent  these  changes  of  temperature,  but  this  precaution  is 
unnecessary  if  proper  care  is  exercised. 

50.  Results  of  Specific-Gravity  Tests. — The  specific 
gravity  of  well-burned  Portland  cement  averages  about  3.15 
and  should  not  fall  below  3.1.  If  it  falls  below  3.1,  tests 
should  also  be  made  on  dried  and  on  ignited  samples  to 
ascertain  whether  or  not  this  condition  has  been  produced  by 
reason  of  excessive  seasoning.  The  specific  gravity  should 
generally  be  taken  only  as  an  indication  of  the  quality  of  the 
cement,  and  the  rejection  of  a  shipment  on  the  ground  of 
failure  in  this  test  is  rarely,  if  ever,  justifiable,  unless  of 
course,  that  failure  has  been  caused  by  adulteration  or 
underburning.  As  a  rule,  low  specific  gravity  merely  indi¬ 
cates  well-seasoned  cement,  and  if  sound  and  sufficiently 
strong,  such  cement  is  the  best  sort  of  material  for  use,  as 
its  durability  is  scarcely  open  to  question. 


CHEMICAL  ANALYSIS 

51.  The  chemical  analysis  of  cement  is  made  by 
methods  that  in  all  essential  particulars  are  similar  to  those 
used  for  limestone  or  for  feldspar,  and,  as  these  tests  are 
rarely  made,  no  explanation  is  required.  Portland  cement 
consists  primarily  of  silica,  alumina,  and  lime,  but  determi¬ 
nations  of  the  proportions  of  these  ingredients  give  little  or 
no  information  as  to  the  quality  of  the  product,  for  the  most 
perfect  combination  of  ingredients  may  be  so  treated  by 
underburning  or  otherwise  as  to  result  in  a  worthless  mate¬ 
rial,  while,  by  careful  treatment,  good  cement  may  be  made 


§35 


TESTS  ON  CEMENT 


35 


from  somewhat  poorly  proportioned  raw  material.  Further¬ 
more,  the  ash  from  the  fuel  in  burning  enters  into  the  analy¬ 
sis  and  will  often  so  modify  the  results  as  to  destroy  their 
significance.  While  chemical  analysis  of  the  essential  ingre¬ 
dients  is  necessary  to  the  manufacturer  for  the  control  of  his 
product,  it  is  of  little  or  no  value  to  the  consumer,  and  gives 
practically  no  indication  of  the  constructive  value  of  the 
cement. 

I 

52.  Determinations  of  certain  ingredients,  notably  mag¬ 
nesia  and  sulphuric  acid,  are  sometimes  valuable,  because, 
under  certain  conditions,  excess  of  these  elements  may  pro¬ 
duce  unsoundness  or  disintegration  of  the  product.  It  is 
especially  necessary  for  construction  that  is  to  be  placed  in 
sea-water  that  these  two  substances  be  kept  within  the  speci¬ 
fied  limits,  for  their  deleterious  effect  reaches  a  maximum 
when  placed  in  this  situation.  Under  such  circumstances, 
analysis  for  magnesia  or  sulphuric  acid  may  be  made  at 
times,  but,  for  ordinary  conditions,  the  test  is  absolutely 
unnecessary,  any  injurious  properties  being  shown  much 
more  clearly  in  the  physical  tests  than  by  analysis.  The 
limits  of  magnesia  and  sulphuric  acid  in  Portland  cement 
are  commonly  placed  at  4  per  cent,  for  the  former  and 
1.75  per  cent,  for  the  latter.  Complete  ultimate  analysis  of 
Portland  cement  will  usually  give  results  within  the  following 
limits: 


Per 

Cent. 

Silica,  Si02 . .  .  . 

20.0 

to 

24.0 

Alumina,  Ala03  . 

6.0 

to 

9.0 

Iron  oxide,  Fe203 . 

2.0 

to 

4.0 

Lime,  CaO  . 

59.0 

to 

65.0 

Magnesia,  MgO . .  . 

.5 

to 

5.0 

Sulphuric  acid,  S03 . 

.5 

to 

2.5 

Carbonic  acid  and  water,  C02  -f  H20  . 

1.0 

to 

4.0 

Alkalies,  K20  and  Na20 . 

0.0 

to 

3.0 

I 


36 


TESTS  ON  CEMENT 


35 


NATURAE  AND  STAG  CEMENTS 

53.  The  methods  of  conducting  tests  of  natural  and 
slag  cements  are,  in  all  important  particulars,  identical 
with  those  employed  for  Portland  cement,  although  the 
results  obtained  and  the  interpretation  to  be  put  on  them 
are  often  radically  different.  In  the  testing,  the  only  essen¬ 
tial  difference  is  in  the  amount  of  water  required  by  these 
cements  to  produce  normal  consistency,  natural  cement 
requiring  from  23  to  35  per  cent,  and  slag  cement  taking 
about  18  per  cent.,  or  on  an  average  of  2  or  3  per  cent,  less 
than  Portland.  Tests  of  natural  cement  for  tensile  strength 
are  also  frequently  made  on  1-1  and  1-2  mortars,  but  recent 
practice  is  to  test  mortars  of  all  kinds  of  cement  in  1-3  mix¬ 
tures.  For  these  cements,  moreover,  the  specific-gravity 
test  has  practically  no  significance,  except  in  determining 
the  uniformity  with  which  the  different  brands  are  made. 
The  requirements  for  these  materials  are  given  in  Table  II. 


SPECIFICATIONS 

54.  The  common  requirements  for  high-grade  Port¬ 
land,  natural,  and  slag  cements  are  given  in  Table  II. 
A  complete  modern  specification  for  Portland  cement  is 
here  given.  _____  , 

SPECIFICATIONS  FOR  PORTLAND  CEMENT 

OO.  Kind, — All  cement  shall  be  Portland  of  the  best  quality, 
dry,  and  free  from  lumps.  By  Portland  cement  is  meant  the  finely 
pulverized  product  resulting  from  the  calcination  to  incipient  fusion  of 
an  intimate  mixture  of  properly  proportionated  argillaceous  and  cal¬ 
careous  materials  to  which  no  addition  greater  than  3  per  cent,  has 
been  made  subsequent  to  calcination. 

56.  Packages. — Cement  shall  be  packed  in  strong  cloth  or  can¬ 
vas  bags,  or  in  sound  barrels  lined  with  paper,  which  shall  be  plainly 
marked  with  the  brand  and  the  name  of  the  manufacturer.  Bags 
shall  contain  94  pounds  net  and  barrels  shall  contain  376  pounds  net. 

57.  Inspection. — All  cement  must  be  inspected,  and  may  be 
reinspected  at  any  time.  The  contractor  must  submit  the  cement,  and 


§35 


TESTS  ON  CEMENT 


37 


TABLE  II 

REQUIREMENTS  FOR  HIGH-GRADE  CEMENTS 


Requirements 

Portland 

Cement 

Natural 

Cement 

Slag 

Cement 

Specific  gravity :  Not  less 

than . 

3-1 

2.8 

2.7 

Fineness: 

Residue  on  No.  ioo  sieve, 

not  over . 

8% 

10% 

3% 

Residue  on  No.  200  sieve, 

not  over . 

25% 

30% 

10% 

Time  of  setting: 

Initial,  not  less  than  .  . 

20  min. 

10  min. 

20  min. 

Hard,  not  less  than  .  .  . 

1  hr. 

30  min. 

1  hr. 

Hard,  not  more  than  .  . 
Te?isile  strength  per  square 

10  hr. 

3  hr. 

10  hr. 

inch  : 

7  days,  neat,  not  less  than 
28  days,  neat,  not  less 

500  lb. 

125  lb. 

35o  lb. 

than . 

600  lb. 

225  lb. 

450  lb. 

7  days,  1-3  quartz,  not 

• 

less  than . 

170  lb. 

50  lb. 

125  lb. 

28  days,  1-3  quartz,  not 

less  than . 

•240  lb. 

1 10  lb. 

200  lb. 

So2i?id?iess  : 

Normal  pats  in  air  andj 

sound  and 

sound  and 

sound  and 

water  for  28  days  to  bel 

hard 

hard 

hard 

Boiling  test  to  be  .  .  .  j 

sound  and 
hard 

sound  and 

hard 

Analysis: 

Magnesia,  A/gO,  not  over 
Anhydrous  sulphuric 

4% 

4% 

acid,  S03,  not  over  .  . 
Sulphur,  S ,  not  over  .  . 

1.75% 

1.3% 

38 


TESTS  ON  CEMENT 


§35 


afford  every  facility  for  inspection  and  testing,  at  least  12  days  before 
desiring  to  use  it.  The  chief  engineer  shall  be  notified  at  once  on 
receipt  of  each  shipment  at  the  work.  No  cement  will  be  inspected 
or  allowed  to  be  used  unless  delivered  in  suitable  packages  properly 
branded.  Rejected  cement  must  be  immediately  removed  from  the 
work. 

58.  Protection. —The  cement  must  be  protected  in  a  suitable 
building  having  a  wooden  floor  raised  from  the  ground,  or  on  a 
wooden  platform  properly  protected  with  canvas.  It  shall  be  stored 
so  that  each  shipment  will  be  separate,  and  each  lot  shall  be  tagged 
with  identifying  number  and  date  of  receipt. 

59.  Quality  . — The  acceptance  or  rejection  of  a  cement  to  be 


used  will  be  based  on  the  following  requirements: 

Specific  gravity:  Not  less  than  3.1. 

Ultimate  tensile  strength  per  square  inch:  Pounds 

7  days  (1  day  in  air,  6  days  in  water) . 500 

28  days  (1  day  in  air,  27  days  in  water) . 600 

7  days  (1  day  in  air,  6  days  in  water),  1  part  cement 

to  3  parts  of  standard  quartz  sand . 170 

28  days  (1  day  in  air,  27  days  in  water),  1  part  of 
cement  to  3  parts  of  standard  quartz  sand  ....  240 


Fineness:  Residue  on  No.  100  sieve  not  over  8  per  cent.,  by  weight; 
residue  on  No.  200  sieve  not  over  25  per  cent.,  by  weight. 

Set:  It  shall  require  at  least  20  minutes  to  develop  initial  set,  and 
shall  develop  hard  set  in  not  less  than  1  hour  nor  more  than  10  hours. 
These  requirements  may  be  modified  where  the  conditions  of  use 
make  it  desirable. 

Constancy  of  Volume:  Pats  of  cement  3  inches  in  diameter,  ^  inch 
thick  at  center  tapering  to  thin  edge,  immersed  in  water  after  24  hours 
in  moist  air,  shall  show  no  signs  of  cracking,  distortion,  or  disinte¬ 
gration.  Similar  pats  in  air  shall  also  remain  sound  and  hard.  The 
cement  shall  pass  such  accelerated  tests  as  the  chief  engineer  may 
determine. 

Analysis:  Sulphuric  anhydride,  S03,  not  more  than  1.75  per  cent.; 
magnesia,  MgO,  not  more  than  4  per  cent. 


CONCRETE  BUILDING  BLOCKS 

(PART  1) 


INTRODUCTION 

1.  Definition. — A  concrete  block  is  a  building  unit 
formed  from  a  combination  of  cement  and  aggregate  mixed 
with  water  and  molded  into  required  form. 

This  definition  is  much  broader  than  one  that  might  cover 
the  ordinary  commercial  concrete  block,  but  the  subject  must 
be  looked  at  broadly  in  order  to  get  proper  bearings  and  to 
secure  a  proper  realization  of  the  place  that  the  concrete 
block  occupies  with  respect  to  the  cement  and  concrete 
industries. 

2.  History. — Concrete  blocks  are  generally  regarded  as 
something  new,  and  the  industry  appears  to  most  persons 
as  too  young  to  merit  that  confidence  accorded  to  forms  of 
construction  with  which  they  are  more  familiar.  This  new¬ 
ness  is  real  only  in  so  far  as  it  applies  to  the  particular  forms 
of  block  recently  introduced,  or  to  the  particular  processes  of 
manufacture  that  have  been  developed  to  meet  the  needs 
of  the  industry  during  its  half  dozen  years  of  activity. 

By  carefully  looking  into  the  history  of  building  among 
many  ancient  and  modern  peoples,  it  will  be  found  that 
concrete  blocks  were  used  for  certain  structural  purposes. 
Although  the  composition  of  the  concrete  does  not  accord 
with  present  practice — cinders,  pieces  of  brick,  and  various 
hard  substances  were  often  used  instead  of  gravel  or  broken 
stone — it  may  be  said  that,  in  general,  the  substance  approx¬ 
imates  the  present  conception  of  cement.  In  fact,  every- 

COPYRIQHTEO  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS'  HALL,  LONDON 

§  36 


211—21 


2 


CONCRETE  BUILDING  BLOCKS 


§36 


where  in  the  ruins  of  ancient  works  are  found  blocks  of  con¬ 
crete  whose  durability,  after  the  lapse  of  centuries,  challenges 
modern  skill. 

In  the  middle  ages  similar  blocks  were  used  in  fortifications 
and  other  work  whenever  it  was  more  convenient  to  transport 
the  manufactured  blocks  than  to  make  the  concrete  in  place. 
In  many  places  in  England  such  blocks  were  substituted  for 
stone,  and  in  the  United  States,  very  early  in  the  19th  cen¬ 
tury,  they  were  used  for  residence  construction. 

In  all  the  instances  mentioned,  the  use  of  concrete  blocks 
was  limited,  and  the  walls,  as  well  as  the  blocks  themselves, 
were  made  solid.  A  hollow  wall,  it  seems,  was  not  thought 
of  until  the  middle  of  the  19th  century,  when  hollow  blocks 
came  into  use.  Even  then,  instead  of  utilizing  the  air  space 
as  insulation,  the  builders  imagined  that  it  had  to  be  filled 
with  some  deadening  material. 

3.  It  is  unfortunate  that  the  early  efforts  of  block  con¬ 
struction  in  the  United  States  were  along  the  line  of  a  cement- 
and-fine-sand  mixture,  so  that  cement  blocks  was  the  term  by 
which  they  were  designated.  So  far  as  is  known,  no  effort 
was  made  to  use  a  coarser  material,  making  true  concrete, 
earlier  than  1902,  and  it  was  some  2  or  3  years  later  before 
the  term  concrete  block  came  into  general  use. 

About  the  same  time  there  arose  among  block  makers  a 
strong  desire  to  imitate  natural-stone  effects,  and  the  term 
artificial  stone  took  a  firm  hold,  from  which  it  was  not  easily 
dislodged.  To  persons  already  familiar  with  the  extensive 
use  of  concrete  and  the  variety  of  its  surface  finish,  this  may 
seem  strange.  However,  it  must  be  remembered  that  the 
concrete-block  industry,  which  is  now  well  known  throughout 
America,  developed,  within  a  few  years,  from  almost  nothing, 
and,  besides,  during  the  labors  of  the  early  block  makers 
reinforced  concrete,  armored  concrete,  and  ferroconcrete  were 
likewise  striving  for  a  name  and  a  place.  In  short,  no  one 
seemed  to  be  aware  of  the  merits  of  concrete  blocks  for  build¬ 
ing  purposes,  and  for  this  reason  they  were  not  used  except 
as  a  cheap  imitation  of  stone.  This  stage,  with  its  delusions, 


§30 


CONCRETE  BUILDING  BLOCKS 


3 


has  passed,  and  the  concrete  block  is  now  valued  for  its  own 
distinctive  qualities. 

4.  Use  aiul  Efficiency. — To  the  fair-minded  person, 
it  is  apparent  that  there  is  a  large  field  for  both  reinforced 
concrete  and  concrete  blocks.  One  of  these  forms  of  con¬ 
struction,  however,  cannot  entirely  replace  the  other. 
Although  the  efficiency  of  blocks  cannot  be  questioned,  it 
would  be  short-sighted  not  to  recognize  their  limitations  and  to 
note  the  greater  efficiency  of  reinforced  concrete  in  such  struc¬ 
tures  as  the  Ingalls  and  Pugh  buildings,  of  Cincinnati,  Ohio, 
or  the  Marlborough-Blenheim  Hotel,  of  Atlantic  City,  New 
Jersey.  There  are  numerous  four-story  buildings  of  concrete 
blocks,  occupied  as  warehouses,  hotels,  office  buildings,  etc., 
that  give  perfect  satisfaction,  and  there  is  no  reason  why 
blocks  should  prove  unsatisfactory  in  six-  or  eight-story  build¬ 
ings.  Above  eight  stories  there  would  hardly  be  any  economy 
in  their  use,  nor  any  other  advantage  adequately  offsetting 
the  increased  cost  resulting  from  the  use  of  the  heavier  walls 
required  in  a  higher  building. 

There  are,  however,  places  where  blocks  are  distinctly 
advantageous  and  those  places  are  in  dwellings  and  in  two-, 
three-,  and  four-story  business  buildings.  In  all  such  build¬ 
ings,  the  walls  may,  with  perfect  safety,  be  comparatively 
light  and  the  blocks  still  afford  the  usual  factor  of  safety  in 
reference  to  loading  of  floors.  Consequently,  the  cost  may  be 
kept  below  that  of  any  other  construction  of  equal  quality. 
It  is  in  the  construction  of  homes  that  the  concrete  block  is 
of  greatest  use,  and  as  the  methods  of  manufacturing  and 
using  the  blocks  are  studied  in  detail  the  reasons  for  this  will 
be  more  clearly  seen. 


4 


CONCRETE  BUILDING  BLOCKS 


§36 


MANUFACTURE  OF  CONCRETE  BLOCKS 


CONCRETE  BLOCKS  IN  GENERAL 


SHAPE  OF  BLOCKS 

5.  The  accepted  shape  of  the  concrete  block  is  such  that 
its  exposed  surface  is  a  rectangle.  The  block  may  extend 
through  the  wall,  or  it  may  not.  In  every  case,  provision  is 
made  for  an  air  space  in  the  wall,  and  the  means  by  which 
this  is  accomplished  varies  widely  and  is  covered  by  many 
patents. 


6.  One-Piece  Blocks. — Blocks  that  extend  through 
a  wall  are  termed  one-piece  blocks.  The  outer  part  is 
called  the  face  section ;  the  inner  part,  the  back  section;  and  the 
partitions  that  unite  the  face  section  to  the  back,  the  webs ,  or 
withes.  All  such  blocks  are  correctly  termed  hollow  blocks. 

Fig.  1  shows  a  gen¬ 
eral  form  of  a  one- 
piece  hollow  block. 
The  face  section  of 
this  block  is  shown 
at  a;  the  web,  at  6; 
the  hollow  spaces,  at 
c\  and  the  back  sec¬ 
tion  at  d.  The  space 
Fig.  i  in  one  block  connects 

with  those  in  succeeding  and  preceding  courses,  forming  a 
continuous  air  space  from  the  top  to  the  bottom  of  the  wall. 
Of  course,  different  types  of  one-piece  blocks  may  differ 
somewhat  from  this  standard. 


§  30 


CONCRETE  BUILDING  BLOCKS 


5 


7.  In  hollow  blocks,  the  number  of  webs  on  each  block 
may  vary  from  two  to  four  or  more;  three  is  the  common 


number,  as  it  affords  two  or,  as  in  Fig.  1,  three  hollow  spaces. 
The  fact  that  this  form  was  the  earlier  and  the  more  common 


Fig.  3 


has  contributed  to  the  general  impression  that  all  concrete 
blocks  are  hollow  blocks,  while  in  many  later  forms  it  is  not 


Fig.  4 


the  block,  but  the  wall,  as  a  result  of  the  arrangement  of  the 
blocks,  that  is  hollow. 


CONCRETE  BUILDING  BLOCKS 


6 


8.  Two-Piece  Blocks. — Blocks  in  which  the  face 
section  and  back  section  constitute  two  separate  parts  are 


Fig.  5 


known  as  two-piece  blocks.  The  walls  made  of  these 

blocks  may  be  spoken 
of  as  two-piece  walls. 
These  blocks  are  of  a 
great  variety  of  forms 
and  are  often  patented. 
The  more  common  forms 
are  designated  as  T 
shape,  L  shape,  and  U 
shape,  because  their 
general  outlines  conform  to  the  shape  of  these  letters.  Figs.  2, 


Fig.  7 


3,  and  4  illustrate  walls  made  of  T-,  L-,  and  U-shaped 
blocks,  respectively. 


CONCRETE  BUILDING  BLOCKS 


7 


§  36 


9.  Fig.  5  shows  a  wall  that  is  also  made  up  of  U-shaped 
blocks.  These  blocks,  however,  are  laid  crosswise  instead  of 
lengthwise. 


Fig.  8 


The  type  of  block  used  in  the  wall  shown  in  Fig.  6  may  be 
considered  as  an  unsymmetrical  form  of  the  T-shaped  block. 

In  laying  two-piece  walls,  the  blocks  on  the  back  of  the 
wall  break  joints  with  those  on  the  front,  so  that  the  only 
joints  extending  through  the  wall  are  the  horizontal  ones 
between  the  courses. 

In  Fig.  7  is  shown  a  form  of  block  that  is  a  revival,  in  modi¬ 
fied  form,  of  a  very  old  style  in  which  two  brick-shaped  slabs, 
one  forming  the  face  and  the  other  the  back,  are  joined  by 
metal  ties  a  laid  in  mortar  on  top  of  each  course.  This  gives 
the  general  effect  of  a  one-piece  block,  the  only  difference 


being  a  continuous  air  space  throughout  the  wall,  as  the  trans¬ 
verse  webs  are  omitted,  the  metal  ties  performing  their  function. 


8 


CONCRETE  BUILDING  BLOCKS 


§36 


Another  type  of  two-piece  block  that  produces  a  continu¬ 
ous  air  space  is  shown  in  Fig.  8.  Each  pair  of  blocks  is 
permanently  united  by  means  of  four  rods  a,  that  are 
embedded  during  the  forming  process. 

Fig.  9  illustrates  a  type  of  two-piece  wall  in  which  the  face 
and  back  portions  of  the  blocks  are  laid  entirely  separate, 
the  two  halves  of  the  wall  being  connected  by  headers  a. 


The  wall  shown  in  Fig.  10  is  built  up  of  blocks  that  are 
triangular  in  shape.  As  indicated  by  the  arrows,  there  is  a 
very  free  passage  of  air  through  the  blocks,  in  both  horizontal 
and  vertical  directions. 


SIZE  AND  WEIGHT  OF  BLOCKS 

10.  Size. — The  size  of  a  concrete  block  in  respect  to 
the  distance  from  the  face  section  to  the  back  is  variable, 
because  the  width  is  regulated  by  the  required  thickness  of 
wall.  This  dimension  can  be  changed  by  lengthening  or 
shortening  the  connecting  webs.  It  is  customary,  however, 
in  wider  walls  to  make  some  variation  in  the  thickness  of 
the  face  section  and  the  back,  as  in  this  way  a  larger  bearing 
surface  is  afforded;  in  addition,  better  construction  is  secured 
by  increased  resistance  to  torsion  or  unequal  expansion  in  case 
of  excessive  heating  of  one  side  of  the  wall.  On  the  other 


CONCRETE  BUILDING  BLOCKS 


9 


§36 

hand,  the  decrease  in  thickness  of  face  section  and  the  back 
in  narrow  walls  carrying  light  weight  not  only  serves  to 
increase  the  insulation  afforded  by  the  interior  air  space,  but 
also  effects  some  saving  of  material.  The  width  of  walls  as 
customarily  specified  are  as  given  in  Table  1. 

1  1 .  The  size  of  the  blocks  in  respect  to  the  length  and 
height  are  determined  by  three  factors:  (1)  Facility  in 
handling  and  laying;  (2)  preservation  of  a  unit  system;  and 
(3)  appearance  in  the  completed  wall. 

Although  with  the  growth  of  the  industry,  machinery 
manufacturers  have  found  it  necessary  to  provide  a  greater 


TABLE  I 

WIDTH  OF  WALDS  FOR  BUILDINGS  OF  VARIOUS  HEIGHTS 

(Width  of  Partitions,  4  to  6  Inches) 


Kind  of  Building 

Width  of  Walls 

Inches 

Base¬ 

ment 

First 

Story 

Second 

Story 

Third 

Story 

Fourth 

Story 

One  story . 

12-15 

8-10 

Two  story . 

I5~I7 

10-12 

8-10 

Three  story . 

17-20 

12-15 

10-12 

.  8-10 

Four  story . 

20-22 

T5~ x7 

12-15 

10-12 

8-10 

range  of  adjustability,  there  yet  remains  among  the  many 
machines  offered  so  wide  a  difference  as  to  size  that  no  recog¬ 
nized  standard  can  be  said  to  exist. 

The  general  tendency  has  been  to  make  as  large  blocks  as 
possible  in  order  to  reduce  the  manufacturing  cost  per  square 
foot  of  wall.  This  practice  finally  reached  a  point  where  the 
additional  labor  of  handling,  hoisting,  and  laying  more  than 
offset  the  saving  in  molding,  and  as  blocks  came  to  be  used 
in  wider  walls  and  higher  buildings  this  extra  expense  in 
handling  large  blocks  became  more  and  more  burdensome. 
Consequently,  blocks  30  and  32  inches  long  are  becoming  less 


10 


CONCRETE  BUILDING  BLOCKS 


§36 


common,  and  blocks  24,  20,  and  even  16  inches  in  length  are 
gaining  in  favor,  often  being  light  enough  to  be  handled  by 
one  man. 

The  height,  of  courses  is,  or  at  least  should  be,  determined 
by  adherence  to  a  system  of  units.  For  example,  in  using  a 
block  24  inches  in  length,  courses  of  4,  8,  or  12  inches  will 
simplify  construction  and  preserve  ratios  between  surface 
dimensions  that  are  essential  to  correct  building  construction. 

The  end  to  be  sought  in  sizes  chosen,  so  far  as  appearance 
is  concerned,  is  geometrical  symmetry,  and  when  the  pos¬ 
sibilities  afforded  by  the  concrete  block  are  considered,  it  is 
deplorable  that  such  variation  in  sizes  has  been  permitted  in 
many  buildings. 

12.  Weight. — The  weight  of  a  concrete  block  is  deter¬ 
mined  by  its  composition,  its  size,  and  its  percentage  of  air 
space.  The  composition  cannot  be  varied  for  the  sake  of 
reducing  the  weight,  as  that  is  regulated  by  more  important 
considerations.  The  size  and  proportion  of  solid  matter, 
however,  may  be  reduced  to  decrease  the  weight. 

Weight  is  important  because  of  the  cost  of  placing  and 
because  of  the  load  on  the  lower  courses  and  the  foundation. 
A  reduction  in  size,  unless  it  is  a  reduction  in  the  width  of  the 
wall,  cannot  affect  the  load,  but  it  does  affect  the  handling 
cost,  while  an  increased  air  space  affects  both.  On  account 
of  lack  of  established  standards  of  size,  it  is  difficult  to  give 
figures  that  will  apply  to  the  weight  of  blocks  made  on  dif¬ 
ferent  machines.  In  general,  the  aim  should  be  to  keep  the 
weight  low  enough  in  one-piece  blocks  so  that  two  men  can 
handle  a  block  on  the  wall,  and  in  two-piece  walls  so  that  one 
man  can  handle  a  block  without  assistance.  When  this  rule 
is  exceeded,  it  usually  means  paying  an  extra  man,  who  is 
necessarily  idle  half  his  time. 


§  3G 


CONCRETE  BUILDING  BLOCKS 


11 


AIR  SPACE  OF  BLOCKS 

13.  The  air  space  in  the  wall  is  the  indispensable  charac¬ 
teristic  of  concrete-block  construction.  It  is  this  air  space 
that  renders  a  building  warm  in  winter  and  cool  in  summer; 
that  prevents  the  passage  of  moisture  through  a  medium 
that  is  frequently  more  porous  than  it  should  be;  that  pro¬ 
tects  the  contents  of  a  building  from  damage  by  exterior  fire; 
that  deadens  a  wall  against  transmission  of  sound;  and  that 
affords  that  ventilation  which  makes  concrete-block  construc¬ 
tion  thoroughly  sanitary. 

The  air  space  is  the  only  part  of  the  block  that  does  not 
cost  anything,  and  this  cost  saving  was  once  its  strongest 
recommendation . 

14.  There  has  been  a  great  deal  of  argument  about  the 
percentage  of  air  space.  In  order  to  provide  for  the  unequal 
stresses  that  the  front  and  back  of  a  one-piece  block  may 
be  subjected  to,  and  to  preserve  symmetrical  proportions 
between  the  face  section,  the  back,  and  the  several  connecting 
webs,  it  is  difficult  to  provide  an  air  space  exceeding 
33^  per  cent.  It  was  found  that,  assuming  all  concrete 
blocks  to  be  made  of  good  concrete,  the  compressive  strength 
of  a  block  (66§  per  cent,  of  the  bearing  surface  being  solid) 
was  more  than  sufficient.  In  a  wall  built  of  two-piece  blocks 
the  air  space  is  not  controlled  by  the  proportions  of  the 
blocks.  Consequently,  it  is  possible  in  a  two-piece  wall  to 
give  an  air  space  varying  according  to  the  width  of  the  wall 
from  a  minimum  up  to  as  high  as  55  per  cent.  The  per¬ 
centage  of  air  space  is  often  governed  by  city  regulations. 
An  allowance  of  33^  per  cent,  air  space  has  been  suggested. 

15.  In  all  systems  of  block  construction,  the  perpendicular 
spaces  are  arranged  so  as  to  form  vertical  flues  from  the  bot¬ 
tom  of  a  wall  to  its  top.  They  afford,  therefore,  boundless 
possibilities  for  ventilation,  as  well  as  convenient  receptacles 
for  all  sorts  of  pipe  and  wiring.  ' 


12 


CONCRETE  BUILDING  BLOCKS 


§36 


ESSENTIAL  QUALITIES  OF  CONCRETE  BLOCKS 

16.  Strength. — Strength  in  a  building  material  is  usually 
of  three  kinds,  namely,  compressive ,  tensile ,  and  transverse. 

The  compressive  strength  of  concrete  depends  prin¬ 
cipally  on  thorough  filling  of  voids,  and  hence  is  directly 
related  to  density.  The  compressive  strength  of  concrete 
blocks  varies  according  to  the  skill  of  the  individual  manu¬ 
facturer,  and  in  well-made  blocks  it  should  average  over 
2,000  pounds  to  the  square  inch  of  material  subjected  to 
pressure. 

The  tensile  strength  depends  on  the  amount  of 
cement  used  in  the  mixture.  In  average  mixtures  of  concrete, 
this  strength  is  found  to  be  from  one-eighth  to  one-tenth  of 
the  compressive  strength.  Although  concrete  blocks  will 
not  be  subjected  to  pure  tensile  stresses,  they  may  be  exposed 
to  combined  tensile  and  compressive  stresses.  This  is  the 
case  when  a  block  is  carrying  a  heavier  load  on  one  end  than 
on  the  other,  generally  referred  to  as  eccentric  loading.  The 
block  may  then  show  compressive  stresses  at  one  end  and 
tensile  stresses  at  the  other. 

If  the  load  comes  on  one  or  both  ends  of  the  block,  and 
these  are  insufficiently  supported  while  its  middle  is  solidly 
supported,  transverse,  or  bending,  stresses  are  called  into 
action. 

If  the  stresses  are  maintained  up  to  the  point  of  rupture,  it 
will  be  found  that  the  upper  side  has  become  longer  and  the 
lower  side  shorter.  The  lower  side  would  be  amply  safe 
because  of  the  great  resistance  of  the  material  to  compression, 
but  the  upper  side  is  subjected  to  a  tensile  stress  to  which 
is  offered  only  one-eighth  or  one-tenth  of  the  resistance  that 
the  lower  side  is  offering  to  compression.  Hence,  a  crack 
will  open  in  the  top  of  the  block  and  gradually  come  through 
unless  the  stress  is  relieved.  An  unreinforced-concrete  block 
should  therefore  never  be  laid  in  such  position.  When  laid 
truly  in  a  wall,  a  well-made  concrete  block  will  not  fail  to  carry 
its  load,  but  it  must  be  borne  in  mind  that  in  direct  compres¬ 
sion  lies  the  strength  of  the  concrete  block. 


§  3G 


CONCRETE  BUILDING  BLOCKS 


13 


17.  Density. — Density  is  a  quality  that  is  only  indirectly 
of  importance.  As  already  stated,  it  has  a  very  decided  influ¬ 
ence  on  the  compressive  strength.  It  also  affects  the  per¬ 
meability  of  the  block.  But  impermeability  to  water  is  not 
always  directly  proportional  to  density.  The  densest  block 
will  not  always  possess  the  greatest  impermeability,  because 
of  certain  theoretical  considerations  in  regard  to  the  size  of 
the  aggregate;  but  for  practical  purposes,  density  may  be 
considered  as  closely  associated  with  the  power  of  a  block  to 
resist  the  penetration  and  transmission  of  water.  Evidently, 
to  obtain  the  greatest  percentage  of  solids  in  a  block,  it  is  only 
necessary  to  fill  the  voids  between  the  sand  and  the  gravel 
or  other  inert  material.  This  is  by  no  means  a  simple  matter, 
and  will  in  due  course  be  given  the  attention  that  it  deserves 
as  one  of  the  leading  factors  in  the  making  of  good  concrete 
blocks. 

18.  Impermeability.  —  As  used  in  connection  with 
concrete  walls,  impermeability  signifies  the  resistance  offered 
to  the  passage  of  water  by  capillary  attraction.  There  are 
three  ways  in  which  a  wall  may  be  made  impermeable : 
(1)  By  making  a  block  that  will  not  admit  water;  (2)  by  build¬ 
ing  a  wall  so  that  there  will  be  no  path  for  water  to  travel; 
and  (3)  by  waterproofing  the  blocks  or  the  wall. 

To  these  several  methods  greater  attention  will  be  given 
later,  but  here  it  may  be  said  that  one  of  the  most  important 
attributes  of  a  concrete-block  wall  is  its  power  to  produce 
absolutely  waterproof  buildings. 

19.  Durability. —  That  concrete  is  the  most  durable 
of  the  world’s  structural  materials  is  an  authenticated  fact. 
Whether  or  not  as  much  may  be  said  of  concrete  blocks 
depends  on  how  they  are  made  and  how  they  are  used. 

By  studying  the  successes  and  failures  of  others,  much 
available  data  may  be  collected  that  will  indicate  how  to  make 
blocks  of  the  highest  quality  and  how  to  incorporate  such 
blocks  into  buildings  so  that  they  will  withstand  the  ravages 
of  time.  Given  the  factor  of  intelligent  and  conscientious 
manufacture,  supplemented  by  capable  superintendence  of 


14 


CONCRETE  BUILDING  BLOCKS 


§3G 


construction,  there  is  no  reason  why  the  average  concrete- 
block  building  should  be  condemned  short  of  two  or  three 
centuries.  It  is  well  to  draw  clearly  the  line  between  the  bad 
practice  that  has  characterized  much  of  the  concrete-block 
construction  of  the  past  and  the  more  successful  methods  that 
have  come  into  use  and  are  destined  to  inspire  greater  con¬ 
fidence  toward  the  industry.  It  is  only  necessary  to  recall 
the  struggle  with  the  cement  sidewalk,  and  the  miles  of  it  that 
disintegrated  from  defective  material  or  poor  workmanship; 
and  yet,  to-day  the  granitoid  walk  is  recognized  as  the  best 
walk  obtainable.  The  concrete  block  has  had  similar  dif¬ 
ficulties  to  overcome,  and  eventually  it  is  bound  to  be  the 
most  durable  of  building  materials. 

20.  Fire  Resistance. — The  fire-resisting  qualities  of 
concrete  have  been  fairly  wrell  established,  less  by  laboratory 
tests  than  by  the  practical  lessons  taught  by  such  catastrophes 
as  the  Baltimore  fire  and  the  San  Francisco  earthquake. 
As  is  well  known,  concrete  is  not  only  non-combustible, 
but  it  is  a  non-conductor  of  heat  as  well.  In  case  of  a  severe 
conflagration,  its  conductivity  is  still  further  decreased  by 
dehydration  of  the  outer  coating,  usually  about  J  inch  in  an 
intense  fire.  There  can  be  no  stronger  recommendation  for 
the  fire  resistance  of  concrete  than  the  prevalent  practice  of 
fireproofing  structural  steel  by  encasing  it  in  a  coating  of  this 
material.  However,  in  concrete-block  construction  an  addi¬ 
tional  advantage  is  afforded  by  the  air  chamber  in  the  wall; 
this  air  chamber  prevents  the  interior  of  a  wall  from  becoming 
superheated  by  exterior  fire.  Concrete  blocks  are  freely 
criticized  along  this  line,  their  opponents  claiming  that  the 
expansion  of  the  outer  shell  under  fire  exposure  will  cause  the 
block  to  break.  If  blocks  are  well  made,  this  contention  seems 
more  theoretical  than  practical,  and  the  criticism  does  not 
hold  good  at  all  in  the  case  of  two-piece  wails,  where  the 
outer  and  inner  sides  are  not  connected  by  transverse  webs. 

21.  There  have  been  several  cases  in  which  concrete- 
block  buildings  have  not  only  passed  through  fires  unharmed, 
but  have  saved  adjoining  buildings  from  the  flames  and  have 


§36 


CONCRETE  BUILDING  BLOCKS 


15 


likewise  preserved  their  own  contents  from  injury.  In  one 
case,  according  to  reliable  information,  the  interior  of  a  con¬ 
crete-block  building  during  the  progress  of  a  fire  was  so  cool 
that  the  hand  could  be  held  against  the  wall.  When  a  wall 
is  superheated  and  a  stream  of  water  turned  on  it,  it  would 
seem  that  the  sudden  contraction  of  the  concrete  must  cause 
at  least  partial  disintegration,  but  the  facts  do  not  accord  with 
this  theory. 

A  very  remarkable  case  occurred  in  Nashville,  Tennessee, 
in  April,  1907,  when  the  upper  portion  of  the  Montgomery 
Building,  a  four-story  structure  filled  with  furniture,  was 
gutted  by  fire  and  the  walls  in  the  upper  story  were  heated  to 
incandescence.  An  examination  made  the  following  day  by 
the  building  inspector  and  other  persons  showed  that  the 
walls,  with  the  exception  of  a  slight  chipping  of  the  window 
sills  and  a  few  of  the  blocks  adjacent  to  openings,  were  in 
perfect  condition.  This  was  the  more  remarkable  in  view 
of  the  fact,  that  the  walls  were  16  inches  thick  and  50  per  cent, 
hollow,  except  in  the  upper  story  where  they  were  12  inches 
thick  and  about  40  per  cent,  hollow.  Before  this  building 
was  constructed,  its  site  was  occupied  by  a  brick  building 
that  sustained  a  fire  so  badly  that  it  was  necessary  to  tear 
down  the  walls. 

22.  Appearance. — The  appearance  of  a  properly  designed 
concrete-block  building  should  surpass  that  of  any  other 
construction  of  like  cost,  and  yet  concrete-block  structures 
have  been  bitterly  criticized — and  not  without  reason — 
because  of  their  ugliness.  The  sorry  plight  of  much  of  the 
concrete-block  architecture  is  principally  due  to  the  following 
causes: 

(1)  The  desire  to  imitate  other  materials;  (2)  the  lack  of 
variation  in  exterior  form;  (3)  the  faulty  methods  of  manu¬ 
facture;  and  (4)  the  indifference  of  architects. 

23.  The  failure  to  appreciate  the  possibilities  that  the 
concrete  block  possesses  in  itself,  as  well  as  the  desire  to 
imitate  the  exterior  appearance  of  other  building  materials, 
rather  than  to  allow  the  concrete  block  to  rest  upon  its  intrinsic 


16 


CONCRETE  BUILDING  BLOCKS 


36 


merit,  has  developed  an  abnormal  style  of  building  that  is 
neither  stone  nor  brick ;  and  while  it  is  in  a  limited  sense  con¬ 
crete,  it  fails  to  do  justice  to  the  material  of  which  it  is  com¬ 
posed.  The  thought  to  be  grasped  is  that  concrete  blocks 
constitute  a  distinct  class,  and  their  architecture  must  be 
developed  by  due  attention  to  the  possibilities  offered  by  the 
material  in  hand.  Where  this  idea  has  been  kept  in  mind 
the  result  has  been  a  revelation  of  symmetry  and  beauty  and 
a  building  of  characteristic  individuality. 

24.  The  selection  of  a  particular  style  of  block,  for 
instance,  the  prevalent  rock  face,  and  the  use  of  similar  forms 
throughout  a  wall  has  produced  a  tiresome  sameness  of 
design,  offering  no  relief  and  presenting  no  pleasing  contrast 
to  the  eye.  It  is  scarcely  necessary  to  say  that  such  practice 
is  needless  and  that  it  is  being  rapidly  superseded  by  the  intro¬ 
duction  of  such  varied  forms  as  give  to  the  modern  concrete- 
block  building  an  appearance  that  will  compare  favorably 
with  buildings  made  of  more  expensive  material. 

It  must  be  understood  that  the  dark,  smudgy,  porous,  or 
plastered  look  of  many  concrete-block  walls  is  merely  a  matter 
of  ignorance  or  carelessness  in  manufacture,  and  not  a  thing 
that  should  be  associated  with  the  concrete  block  that  is 
rightly  made. 

The  fact  that  architects  have. given  but  little  attention  to 
the  concrete  block  as  affording  a  distinct  style  in  construction 
has  made  it  necessary  for  concrete-block  contractors  to  rely 
upon  their  own  resources,  and  as  these  have  been  limited,  the 
results  have  not  been  pleasing.  This  is  a  matter  for  which 
time  is  the  surest  remedy,  and  already  the  demand  for  block 
buildings  is  drawing  to  their  support,  and  to  the  correction 
of  early  evils,  the  skill  of  some  of  the  most  reputable  architects. 


CONCRETE  BUILDING  BLOCKS 


17 


§36 

FACTORS  AFFECTING  THE  QUALITY  OF  CONCRETE 

BLOCKS 

25.  Composition. — Among  the  factors  that  determine 
whether  a  concrete  block  shall  be  good  or  bad,  the  composition 
of  the  block  naturally  appeals  as  one  of  the  most  vital.  In  the 
early  days  of  the  industry,  all  blocks  were  made  of  fine 
sand  and  cement,  and  this  practice  is  yet  common.  Such 
material  makes  a  mortar  block,  while  a  concrete  block  is 
composed  of  a  fair  proportion  of  gravel  or  broken  stone,  with 
sufficient  finer  material — either  sand  or  pulverized  stone — to 
fill  the  spaces  between  the  larger  ingredients  in  a  thorough 
manner  and  enough  cement  to  bond  the  whole  mass  together 
firmly. 

There  seems  to  be  some  misapprehension  in  regard  to  the 
term  aggregate.  It  is  well,  however,  to  note  that  this  term 
properly  includes  all  the  material  in  a  block  except  the  cement 
and  water,  so  that  it  may  with  propriety  be  divided  into  fine 
and  coarse  aggregate.  A  just  appreciation  of  the  relation  of 
fine  and  coarse  materials  and  the  maintenance  of  uniform  and 
proper  proportions  between  them  goes  far  toward  success  in 
block  making.  It  is  evident  that  skimping  cement  is  a  prac¬ 
tice  that  no  wise  operator  will  countenance,  as  the  result  is 
always  disastrous,  yet  there  are  certain  principles  of  concrete 
making  that  effect  an  enormous  saving  in  cement  without 
loss  of  quality. 

26.  Moisture. — The  use  of  the  correct  amount  of  water, 
at  the  proper  time,  is  a  fundamental  principle  of  block  making. 
A  mixture  too  dry  to  secure  the  initial  set  of  cement  can  never 
give  a  good  block,  and  it  is  equally  important  that  the  block 
be  constantly,  uniformly,  and  adequately  moistened  during 
the  curing  period  that  follows  its  molding. 

27.  m  ixin#. — The  thorough  mixing  of  all  the  ingredients 
is  one  of  the  most  essential  things  in  block  making.  Theo¬ 
retically,  every  particle  of  the  aggregate  must  be  cement- 
coated,  and  this  can  only  be  effected  by  mixing  much  more 
thoroughly  than  is  common. 

211—22 


18 


CONCRETE  BUILDING  BLOCKS 


§36 


28.  Condensation. — After  the  various  ingredients  have 
been  well  mixed,  they  are  deposited  in  a  mold,  and  no  block 
can  come  from  the  mold  strong,  dense,  and  impervious  unless 
it  has  been  condensed  to  such  a  degree  that  air  is  practically 
eliminated.  The  methods  of  condensation  differ,  but  no 
matter  what  method  is  used,  the  condensation  must  be  very 
thorough. 

29.  Curing. — The  forming  of  the  block  is  only  the  initial 
process  of  its  manufacture.  The  curing  period,  which  follows, 
is  the  most  critical  period  in  determining  the  quality  of  the 
finished  block.  The  greater  emphasis  must  be  placed  on  cur¬ 
ing,  because  it  is  so  easily  slighted.  There  is  a  common  belief 
that  blocks  should  be  allowed  to  dry  out  for  a  week  or  two  after 
molding.  This  notion  is  erroneous. 


MATERIALS  OF  MANUFACTURE 

30.  Cement.  — Cement  is  a  very  ancient  product. 
Natural  cement  is  produced  by  burning  natural-cement  rock 
as  found  in  various  localities.  Puzzolan  cement  is  made  by 
grinding  together  hydrated  lime  and  furnace  slag  without 
subsequent  burning. 

Portland  cement ,  as  stated  in  another  Section,  is  made  by 
grinding  together  definite  proportions  of  material  containing 
lime  and  clay,  then  burning  the  mixture  at  intense  heat,  and 
afterwards  grinding  the  clinker  to  a  very  fine  powder.  The 
process  of  manufacturing  Portland  cement  has  been  brought 
to  great  perfection.  The  materials  are  selected  and  propor¬ 
tioned  by  chemical  analysis,  the  burning  is  under  constant 
control,  and  the  grinding  is  effected  by  machinery  especially 
designed  for  the  purpose.  The  rotary  kiln  and  the  Griffin 
mill  have  been  the  great  factors  in  the  development  of  the 
Portland-cement  industry  in  America.  Their  efficiency  has 
multiplied  the  number  of  factories,  has  reduced  the  cost  of 
manufacture,  and  has  raised  the  standard  of  quality  until 
American  Portland  cements  are  today  unrivaled  in  the 
markets  of  the  world. 


CONCRETE  BUILDING  BLOCKS 


19 


§36 

A  very  recent  product  is  the  white  Portland  cement ,  which 
is  manufactured  at  several  places  in  the  United  States.  It  is 
recommended  for  use  in  facing  blocks  because  of  its  lighter 
color  and  its  waterproofing  power.  It  is  an  expensive 
product,  however,  and  is  only  suitable  for  special  purposes. 

31.  Sand. — The  sand  used  in  concrete  blocks  should  be 
clean  and  free  from  clay  or  loam.  For  this  reason,  river  or 
creek  sand  is  usually  preferable  to  bank  sand,  although  bank 
sand  is  sometimes  free  from  foreign  matter.  If  the  sand  is  not 
clean,  it  should  be  washed  before  using.  Sand  should  pref¬ 
erably  be  round  and,  except  for  facing,  should  be  fairly 
coarse.  The  best  sand  is  hard  and  not  all  of  one  size,  but  has 
some  grains  larger  than  others. 

32.  Gravel. — A  hard,  clean  gravel  is  very  desirable  in 
block  making.  Irregularity  in  size  is  an  advantage.  The 
gravel  will  usually  be  mixed  with  sand  and,  provided  there  is 
no  foreign  matter  in  the  natural  mixture,  it  may  be  used  with¬ 
out  screening  by  adding  the  required  amount  of  sand  or  gravel, 
as  the  case  may  be,  to  secure  desired  relative  proportions 
between  fine  and  coarse  aggregate.  If  the  gravel  runs  over 
£  inch  in  diameter,  it  will  be  necessary  to  screen  out  the  larger 
sizes,  but  £  inch  sizes  can  be  used  in  most  block  molds.  It 
is  always  an  advantage  to  use  as  large  a  size  as  can  be  con¬ 
veniently  worked  in  the  mold. 

33.  Stone. — Broken  stone  affords  a  good  material  for 
concrete-block  work.  Limestone  is  very  desirable.  Its  only 
fault  is  that  it  is  liable  to  disintegrate  in  fire  unless  thoroughly 
coated  with  cement.  The  softer  sandstones  are  not  so  good, 
because  a  concrete  cannot,  in  the  nature  of  things,  exceed  the 
strength  of  its  aggregate.  Granite  and  trap  rock  are  the  best 
materials  obtainable,  but  in  some  localities  their  cost  is 
prohibitive. 

It  has  generally  been  found  that  there  is  very  little  dif¬ 
ference  between  the  strength  of  stone  and  gravel  concretes 
after  6  months  or  a  year,  but  at  shorter  periods  the  stone  has 
the  advantage.  This  is  doubtless  due  to  the  fact  that  the 


20 


CONCRETE  BUILDING  BLOCKS 


§36 


irregular  shape  of  broken  stone  offers  a  somewhat  better 
bonding  surface  for  the  cement. 

34.  Water. — The  water  used  in  block  manufacture  should 
be  clean  and  especially  free  from  injurious  minerals  and 
animal  or  vegetable  matter.  Most  persons  think  that  any 
kind  of  water  is  good  enough  for  mixing  concrete.  However, 
the  same  care  should  be  given  to  mixing  water  as  is  given  to 
drinking  water,  and  no  less  care  should  be  given  to  the  water 
used  in  sprinkling  blocks  while  curing. 

35.  Hydrated  Dime. — Hydrated  lime  has  been  generally 
recommended  for  displacing  part  of  the  cement  in  a  block. 
This  material  is  now  extensively  manufactured,  looks  like 
flour,  is  sold  in  sacks,  and  costs  about  the  same  as  cement. 
Its  recommendation  was  prompted  by  a  desire  to  secure 
greater  density  and  impermeability  in  the  block.  Its  addition 
is  of  greater  benefit  to  a  mixture  that  is  poorly  graded  or  low 
in  cement  than  to  one  that  is  rich  in  cement  and  so  propor¬ 
tioned  as  to  fine  and  coarse  aggregate  that  voids  are  reduced 
to  the  minimum.  Before  employing  it,  a  good  plan  is  to 
secure  a  few  pounds  and  note  the  difference  resulting  from 
its  incorporation  in  the  mixture.  A  mixture  of  1  part  of 
hydrated  lime  and  4  parts  of  cement  will  be  safe,  and  in 
some  cases  beneficial,  but  reliance  must  be  placed  rather  on 
careful  proportioning,  thorough  mixing,  and  adequate  con¬ 
densation  than  on  the  addition  of  any  ingredient  to  over¬ 
come  the  result  of  neglecting  these  elementary  principles  of 
concrete-block  manufacture. 

36.  Waterproofing  Compounds.  —  Various  water¬ 
proofing  compounds  are  used  in  the  making  of  concrete 
blocks,  some  of  which  are  mixed  with  cement  in  the  same 
manner  as  hydrated  lime.  These  compounds  are  generally 
made  by  a  secret  process,  and  their  merits  can  be  judged  only 
by  results.  Some  have  more  worth  than  others,  and  the 
remarks  regarding  hydrated  lime  are  applicable  here,  except 
as  to  the  quantity  to  be  used.  This  is  specified  by  the 
manufacturer  of  each  compound. 


§36 


CONCRETE  BUILDING  BLOCKS 


21 


37.  Salt. — Salt  is  often  added  to  concrete-block  mixtures 
in  freezing  weather,  10  per  cent,  of  the  weight  of  the  mixing 
water  being  generally  considered  harmless.  There  are,  how¬ 
ever,  other  methods  of  satisfactorily  overcoming  the  dif¬ 
ficulties  attendant  upon  winter  work. 

38.  Coloring  Matter. — If  blocks  of  a  particular  color  are 
to  be  produced,  it  is  necessary  to  color  only  the  face  of  the 
block.  The  more  correct  way  to  accomplish  this  is  by  the 
use  of  an  aggregate  of  the  required  color.  This,  however, 
is  sometimes  impracticable,  in  which  event  resort  must  be 
made  to  coloring  matter.  Only  mineral  colors  should  be 
used,  and  even  some  of  these  are  injurious  to  the  action  of 
the  cement.  It  is  good  practice  to  use  the  colors  that  are  now 
manufactured  for  this  particular  purpose  from  a  base  of  iron 
pigment.  These  colors  maybe  purchased  in  the  open  market. 
They  are  backed  by  reputable  manufacturers  from  whom 
directions  for  their  use  may  be  obtained.  In  the  use  of  color¬ 
ing  matter,  it  is  well  to  remember  that  the  shade  will  always 
be  lighter  in  a  cured  block  than  in  one  freshly  molded ;  hence, 
the  color  must  be  made  deeper  than  the  one  desired  in  the 
finished  work. 


MANUFACTURING  PROCESSES 


INSPECTION  OF  MATERIALS 

39.  The  inspection  of  materials  for  concrete-block  work 
comprises  the  careful  selection  from  available  supplies  of 
those  best  suited  to  the  manufacturer’s  needs,  and  the  testing 
of  these  materials  from  time  to  time  to  ascertain  that  there  is 
no  falling  away  from  the  established  standard. 

The  choice  between  gravel  and  broken  stone  often  depends 
on  local  availability  and  relative  cost.  However,  the  material 
that  is  selected  must  be  the  best  readily  at  hand  in  point  of 
strength  and  freedom  from  loam,  clay,  or  other  foreign  mate¬ 
rial.  Due  attention  must  also  be  paid  to  its  size,  and,  if  neces¬ 
sary,  suitable  screening  facilities  should  be  provided. 


22 


CONCRETE  BUILDING  BLOCKS 


§30 


40.  Selection  of  Sand. — In  the  matter  of  sand  for 
the  major  portion  of  the  work,  care  must  be  taken  that  the 
sand  is  not  only  clean,  but  reasonably  coarse  as  well.  Of  the 
sand  submitted  for  concrete-block  work,  it  is  often  unnecessary 
to  do  more  than  throw  a  little  into  a  glass  half  full  of  water 
and  stir  for  2  or  3  minutes  to  prove  that  there  is  a  percentage 
of  mud  that  would  render  it,  unless  washed,  unfit  for  use. 

The  more  expensive  grades  of  sand  or  marble  dust  used 
for  facing  blocks  may,  if  necessary,  be  shipped  some  distance, 
as  the  small  amount  used  and  the  a'dded  value  of  a  block 
with  particularly  fine  finish  justify  this  additional  expenditure. 
These  finer  grades  of  sand  can  be  procured  from  any  sand 
company. 

41.  Selection  of  Cement. — Of  the  selection  of  cement 
a  great  deal  might  be  written.  American  Portland  cements 
have  generally  attained  so  high  a  standard  that  the  manu¬ 
facturer  in  deciding  on  a  brand  may  be  justified  in  letting  his 
decision  largely  be  affected  by  the  freight  rate  from  various 
mills.  But,  when  he  has  selected  a  particular  brand,  he  should 
persevere  in  its  use,  unless  its  quality  falls  below  standard, 
because  changing  from  one  brand  to  another  is  liable  to  cause 
change  of  color  in  the  blocks.  The  difference  between  raw 
materials  used  at  the  various  cement  mills  and  between  the 
proportioning  of  materials  and  details  of  manufacture  cause 
variation  in  time  of  setting  and  in  the  color  of  cement. 

There  are  very  few  concrete-block  makers  that  give 
adequate  attention  to  the  testing  of  cement.  Indeed,  com¬ 
paratively  few  test  it  at  all.  It  is  scarcely  to  be  expected 
that  in  the  average  concrete-block  factory  such  technical 
tests  as  provided  by  the  American  Society  of  Civil  Engi¬ 
neers  or  the  American  Society  for  Testing  Materials  will  be 
employed ;  yet  such  tests  can  be  easily  made,  and  besides  very 
little  apparatus  is  required  to  test  the  constancy  of  volume 
of  the  cement.  The  soundness  of  the  cement  is  also  easily 
tested  by  making  a  few  flat  cakes,  or  pats,  from  each  ship¬ 
ment  as  received,  keeping  these  in  moist  air  for  a  day,  and  then 
immersing  some  in  water,  exposing  some  in  moist  air,  and 


CONCRETE  BUILDING  BLOCKS 


23 


boiling  some  others.  In  the  case  of  the  specimens  in  air  and 
water,  results  are  noted  at  7,  14,  and  28  days.  No  contractor 
would  hazard  the  construction  of  a  reinforced-concrete  build¬ 
ing  without  a  cement  laboratory,  and  it  would  seem  that 
simple  tests  would  raise  the  standard  of  block  manufacture. 


PROPORTIONING  THE  MATERIALS 

42.  Proportioning  is  perhaps  the  most  important,  and  at 
the  same  time  the  least  understood,  of  the  processes  involved 
in  concrete-block  manufacture.  The  theory  of  proportioning 
the  materials  contemplates,  fundamentally,  the  elimination 
of  voids  by  so  grading  the  sizes  of  material  and  so  regulating 
the  quantity  of  each  size  that  each  will  fill  the  voids  between 
the  particles  of  the  next  larger  size. 

For  example,  starting  with  f-inch  gravel,  a  gallon  measure 
is  filled  with  this  material,  and  then  water  is  added  until  it 
is  visible  at  top.  If  the  water  is  poured  from  a  graduated 
measure,  the  volume  added  is  known  at  once,  and  it  will 
approximate  that  of  the  displaced  air.  As  gravel  and  sand 
retain  a  certain  quantity  of  water  after  the  latter  is  poured 
off,  it  would  prevent  a  thorough  mixing  of  the  new  material 
added  and  an  accurate  measuring  of  the  voids.  A  fresh  sam¬ 
ple  of  gravel  and  sand  should  therefore  be  used  for  each  suc¬ 
ceeding  operation.  Next,  to  the  original  quantity  of  f-inch 
gravel,  is  added  a  quantity  of  the  next  finer  material,  say 
f-inch  gravel,  equal  in  volume  to  that  of  the  estimated 
volume  of  voids.  The  mixing  of  the  two  materials  is  con¬ 
tinued  until  the  gravel  of  smaller  size  occupies  the  voids  of  the 
gravel  of  larger  size.  Again  a  measured  quantity  of  water  is 
added,  this  time  a  smaller  one.  A  quantity  of  finer  sand, 
equal  in  volume  to  that  of  the  voids  existing  at  present,  is 
added,  mixed  as  before,  and  the  percentage  of  voids  ascer¬ 
tained.  The  latter  percentage  indicates  the  amount  of 
cement  required  to  fill  the  remaining  voids.  To  each  of  the 
estimated  volumes  of  gravel  and  sand  5  per  cent,  should  be 
added  to  allow  for  inaccuracy  in  testing,  but  10  per  cent, 
should  be  added  to  the  required  percentage  of  cement. 


24 


CONCRETE  BUILDING  BLOCKS 


§36 


This  method  of  determining  voids  is  not  scientifically 
accurate,  but  is  recommended  because  of  its  simplicity  and 
convenience.  It  may  be  checked  up  in  the  following  man¬ 
ner:  When  the  relative  percentages  of  different  materials 
have  been  ascertained,  and  a  quantity  of  dry  aggregate  and 
cement  has  been  thoroughly  mixed,  fill  a  vessel  full  and 
weigh  it.  Then  vary  the  mixture  by  adding  more  of  the  fine 
ingredients  or  more  of  the  coarse  ones,  and  deposit  the  same 
weight  of  material  in  the  vessel  as  before.  The  material  of 
which  a  given  weight  occupies  the  least  space  will  contain  the 
greatest  percentage  of  solid  material  and  the  smallest  per¬ 
centage  of  voids. 

43.  At  first  glance  it  may  appear  sufficient  to  use  sand 
alone  in  place  of  graded  aggregate  to  fill  the  voids.  That  this 
is  not  the  case,  however,  will  be  seen  from  the  proven  fact  that 
the  percentage  of  voids  is  very  nearly  the  same  in  any 
aggregate  of  uniform  size,  be  it  fine  or  coarse.  A  block  of 
solid  granite  has,  of  course,  a  greater  density  than  a  quantity 
of  granite  aggregate  occupying  the  same  space,  but  the 
aggregate  filling  this  space  will  approach  the  former  in  den¬ 
sity  the  more  solid  material  it  is  made  to  contain.  Let  it  be 
supposed  that  the  largest  aggregate  is  1  inch  in  size.  If  the 
next  smaller  one  is  of  a  size  that  is  just  small  enough  to  be 
conveniently  lodged  in  the  voids,  and  if  each  succeeding  smaller 
size  is  chosen  as  large  as  the  remaining  voids  will  admit,  it  is 
clear  that  in  this  case  there  will  be  more  solid  material  in  the 
mixture  than  if  sand  alone  is  used. 

It  follows,  then,  that  the  more  carefully  the  material  is 
screened  into  different  sizes,  and  the  more  carefully  these  are 
proportioned,  the  more’ nearly  perfect  will  be  the  mixture. 

44.  But  not  merely  in  the  matter  of  voids  is  proportion¬ 
ing  of  value.  The  theory  of  all  concrete  work  involves  the 
coating  of  the  aggregate  with  cement,  and  the  bonding  of  each 
particle  of  sand  or  gravel  to  the  next  by  means  of  a  film  of 
crystallized  cement.  If  between  any  two  such  particles  there 
is  no  cement,  the  block  will  be  thereby  weakened.  If  an 
attempt  is  made  to  coat  every  grain  of  a  straight-sand  mix- 


§36 


CONCRETE  BUILDING  BLOCKS 


25 


ture  with  cement,  it  is  evident  that  a  very  large  quantity  of 
cement  will  be  required.  If,  on  the  other  hand,  a  straight- 
sand  mixture  with  the  usual  proportion  of  cement  is  used, 
it  is  impossible  to  coat  every  particle  with  cement,  and  a  weak 
block  will  result.  If  larger  aggregate  in  proper  proportion  is 
introduced,  then,  in  the  first  case,  cement  will  be  saved,  and 
in  the  latter  case  strength  will  be  gained  in  the  finished  block. 

45.  To  one  who  has  grasped  this  theory  of  proportioning 
with  respect  to  either  the  elimination  of  voids  or  to  the  dis¬ 
tribution  of  cement,  it  must  appear  impossible  to  fix  arbi¬ 
trarily  a  proportion  that  will  be  applicable  to  all  the  materials 
available  in  the  many  localities  where  concrete  blocks  are  now 
made,  and  in  the  still  greater  number  of  places  where  they 
will  be  manufactured  within  the  next  few  years. 

It  has  generally  been  customary  in  the  making  of  blocks 
of  sand  and  cement  to  use  a  l-to-4  mixture.  This  is  usually 
written  1-4  and  means,  technically,  1  pound  of  cement  to 
4  pounds  of  sand.  However,  such  a  mixture  is  inaccurately, 
though  almost  universally,  interpreted  to  mean  1  sack  of 
cement  to  4  cubic  feet  of  sand. 

The  proportions  used  in  making  true  concrete  blocks  have 
not  been  so  arbitrarily  fixed.  These  proportions  vary  from 
1-2-4  to  1-2J-4J,  1-3-4,  and  l-3^-6J.  The  last  mixture  is 
applicable  only  in  the  case  of  heavy  blocks  where  a  large 
percentage  of  very  coarse  aggregate  can  be  used. 


MIXING  THE  MATERIALS 

46.  Mixing  by  Hand. — The  kind  of  mixing  required  to 
make  superior  concrete  blocks  involves  something  more  than 
shoveling  for  a  given  period  of  time  and  something  more 
than  running  the  ingredients  through  a  mechanical  mixer. 
If  the  material  is  to  be  mixed  by  hand — and  sometimes 

0 

the  exigencies  of  the  small  manufacturer  demand  that  it 
must  be  so — most  careful  supervision  must  be  exercised. 
A  thorough  turning  over  is  demanded,  not  a  mere  hap¬ 
hazard  shoveling.  If  shovels  are  to  be  used,  they  should  be 
square-pointed  rather  than  round,  but  many  mixers  prefer 


20 


CONCRETE  BUILDING  BLOCKS 


§30 


hoes,  and  others  use  rakes  with  good  effect,  claiming  for 
the  latter  the  advantage  of  separating  the  material  in  a 
manner  impossible  with  shovels,  except  in  a  long  throw. 
An  expert  with  a  hoe  can  give  to  the  concrete  a  motion 
that  not  only  turns  it  over,  but  separates  and  spreads  the 
particles  as  well.  The  only  way  to  secure  the  desired  result 
in  hand  work  is  to  use  a  water-tight  platform  that  is  large 
enough  to  permit  the  entire  mass  to  be  turned  over  from 
its  original  position  into  a  new  pile  and  then  back  again.  If 
turning  the  dry  material  twice  does  not  bring  a  uniform  color 
to  it,  the  operation  must  be  repeated  before  water  is  added. 
In  adding  water,  care  must  be  taken  not  to  dash  it  on  in  such 
quantities  or  with  such  force  as  to  wash  the  cement  from  the 
aggregate,  and  after  t*he  water  is  added,  the  turning  must  be 
continued  until  the  whole  mass  becomes  homogeneous. 
Under  no  circumstances  should  the  batch  that  is  to  be  wet 
be  of  greater  volume  than  can  be  consumed  in  30  minutes,  as 
the  average  cement  takes  its  initial  set  within  that  time,  and 
a  block  that  is  to  be  of  good  quality  must  be  molded  before  the 
initial  set. 

47.  Mixing  by  Machinery. — It  is  desirable  that  a  con¬ 
crete-block  factory  be  equipped  with  a  power  mixer,  as  a  more 
thorough  and  more  uniform  mixture  is  thus  secured,  with  a 
saving  of  labor.  In  mixing  by  machinery,  the  directions  sup¬ 
plied  by  the  manufacturer  should  be  carefully  followed. 

Care  should  be  exercised  in  the  selection  of  a  mixer.  Cer¬ 
tain  mixers  that  operate  well  on  wet  concrete  are  ineffectual 
when  a  drier  concrete  is  used.  A  medium-wet  mixture  is 
usually  employed  for  blocks,  and  a  mixer  should  be  selected 
with  reference  to  this  particular  service. 

48.  The  amount  of  water  to  use  in  the  mix  will  depend 
largely  on  the  type  of  block  machine  to  be  filled.  Some 
machines  can  handle  a  much  wetter  mixture  than  others. 
However,  the  aim  should  always  be  to  use  as  wet  a  mixture 
as  can  be  conveniently  discharged  from  the  mold.  Machine 
mixing  should  be  carefully  studied  until  one  knows  exactly 
how  much  water  may  be  used. 


CONCRETE  BUILDING  BLOCKS 


27 


49.  M  ixing  of  Fine  Facing. — The  mixing  of  fine 
facing  is  a  more  delicate  matter  than  the  mixing  of  concrete 
and  must  be  done  separately.  The  operation  involves  the 
careful  screening  of  the  white  sand,  marble  dust,  or  other 
material  and  the  addition  of  the  cement,  together  with  such 
coloring  matter  as  may  be  used.  All  the  material  should  be 
very  thoroughly  mixed  and  then  slightly  dampened.  It  is 
unnecessary  to  make  the  face  matter  as  wet  as  the  body  of  the 
block,  as  reliance  is  had  upon  surplus  water  in  the  block  to 
permeate  the  face  by  capillary  attraction.  An  exception  to 
this  rule  must  be  made  where  a  waterproofing  compound  is 
used.  A  compound  of  this  kind  will  not  permit  the  water 
from  the  block  to  penetrate  the  face,  and  in  that  case  adequate 
crystallization  cannot  ensue  unless  the  face  matter  has  in 
itself  the  necessary  amount  of  water.  After  the  face  matter 
has  been  wet  and  mixed,  it  will  show  a  tendency  to  roll  up 
into  little  balls  owing  to  the  fineness  and  the  richness  of  the 
mixture  (usually  1-1  to  1-3,  the  latter  preferable  because  it 
is  not  so  liable  to  the  formation  of  crazing  cracks).  This 
tendency  of  the  material  to  form  balls  must  be  overcome  by 
again  screening  the  face  matter  immediately  before  it  is  used. 


DEPOSITING 

50.  By  depositing  is  meant  the  process  of  filling  the 
mold  with  the  materials  of  wdiich  the  block  is  to  be  made. 
This  process  is  not  so  simple  as  might  at  first  appear,  and 
many  of  the  qualities  that  the  final  block  is  to  possess  will 
depend  to  a  great  extent  on  the  care  displayed  during  the 
molding  process. 

The  molds  may  be  of  three  kinds,  depending  on  the  position 
occupied  by  the  face  of  the  block.  If  the  face  is  formed  by 
the  bottom  of  the  mold,  it  is  a  face-down  mold;  if  formed  by 
one  of  the  sides  of  the  mold,  it  is  a  side-face  mold;  and  if 
formed  by  the  cover  of  the  mold,  it  is  a  face-up  mold. 

The  method  of  depositing  the  material  in  the  mold  will 
vary  somewhat  with  the  kind  of  mold  employed.  If  a  side- 
face  mold  is  used,  the  concrete  is  placed  a  little  at  a  time, 


28 


CONCRETE  BUILDING  BLOCKS 


§30 


filling  with  some  care  into  the  corners  and  around  the  cores, 
and  tamping  each  layer  thoroughly  so  that  the  bottom  of  the 
block  will  be  of  like  density  with  the  top.  If  the  block  is  to  be 
faced  with  a  material  different  from  that  used  in  the  body, 
a  thin  partition  is  employed  and  the  face  matter  is  placed 


between  the  partition  and  the  face  plate  and  the  coarse 
material  back  of  the  partition  is  tamped  as  the  latter  is 
gradually  withdrawn. 

51.  Side-Face  Mold. — One  type  of  side-face  mold, 
known  as  a  Miracle  block  machine ,  is  illustrated  in  Fig.  11. 


§36 


CONCRETE  BUILDING  BLOCKS 


29 


The  mold  consists  of  iron  end  plates  a{  and  a2,  the  face  plate  b, 
the  back  plate  c,  and  the  bottom  plate  d.  The  end  and  front 
of  the  back  plates  have  pins  ev  as  shown  in  view  (6),  that 
pass  through  holes  e2  in  the  bottom  plate.  Rods  k  fitted  with 
a  nut  at  one  end  and  a  cam-lever  i  at  the  other  serve  to  lock 
the  face  and  back  plates  together.  By  turning  the  cam- 
levers  outwards,  these  plates  may  be  disengaged  and  removed. 
The  cores  /  are  bolted  to  the  bottom  plate  and  are  made 
tapering  toward  the  upper  end  so  as  to  slide  easily  out  of  the 
formed  block,  or  draw ,  as  it  is  called. 

In  Fig.  11  (a)  the  mold  is  shown  ready  to  receive  the  con¬ 
crete  mixture,  which  is  shoveled  in  and  then  tamped  down 
with  suitable  tamping  tools.  When  the  mold  is  filled,  the 
wooden  pallet  k,  Fig.  11  ( b )  is  slid  lengthwise  over  the 
mold  along  the  flange  l,  view  (a),  so  as  to  remove  any  sur¬ 
plus  material.  This  pallet  is  left  on  top  of  the  mold,  and 
by  means  of  the  handles  g  the  mold  is  turned  over  so  as  to 
occupy  the  position  shown  in  Fig.  11  ( b ).  The  bottom  plate  d 
may  then  be  lifted,  and  the  cores  /  withdrawn  from  the  mold. 
All  the  side  plates  may  also  be  removed  after  unlocking  the 
cam-levers  i.  After  removing  the  plates  the  block  rests 
alone  on  the  pallet  k  and  is  ready  to  be  transferred  to  the 
curing  department.  On  locking  the  plates  together  again, 
the  mold  is  ready  for  another  block. 

52.  Face-Down  Mold. — In  Fig.  12  is  shown  a  type  of 
face-down  mold  known  as  the  Ideal  machine.  There  is  a 
great  variety  of  excellent  machines  in  w'hich  the  face  plate 
forms  the  bottom  of  the  mold,  but  as  the  operation  of  all 
of  them  is  somewhat  similar,  the  one  shown  will  serve  as  an 
example. 

In  view  (a)  the  machine  is  shown  in  its  initial  position, 
ready  to  receive  the  material  for  molding  the  block;  in  view 
(6),  the  block  A  is  shown  formed,  ready  to  be  taken  to  the 
curing  room,  technically  known  as  being  carried  off. 

Referring  to  Fig.  12  (a),  it  will  be  seen  that  the  mold  con¬ 
sists  of  end  plates  ax  and  a2  that  are  hinged  to  the  plate  c. 
The  latter  plate  is  connected  to  a  supporting  stand  q  by  means 


30 


CONCRETE  BUILDING  BLOCKS 


§36 


of  hinges  and  f2,  while  the  plate  b  may  be  connected  to  the 
stand  in  any  suitable  manner  so  as  to  allow  an  easy  inter¬ 


change  with  other  plates.  It  will  be  noticed  that  the  plate  c 
is  backed  by  another  plate  cv  the  latter  serving  as  a  support, 


CONCRETE  BUILDING  BLOCKS 


31 


§36 

or  pallet,  for  the  block  when  it  is  transported  from  the  mold 
while  in  its  plastic  state.  The  end  plates  a1  and  a2  are  locked 
to  the  plate  b  by  means  of  the  cam-levers  ex  e2. 

53.  The  molding  is  begun  by  depositing  about  2  shovel¬ 
fuls  of  the  concrete  mixture  into  the  mold,  using  a  tamping 
tool  for  the  purpose  of  compressing  the  material  If  a  special 
face  mixture  is  to  be  used,  a  sufficient  amount  of  this  mate¬ 
rial,  together  with  a  thin  layer  of  coarse  concrete,  is  first 
deposited,  and  thoroughly  tamped  to  insure  a  bond  between 
the  face  and  the  body  of  the  block.  The  cores  o  are  then 
moved  forwards  by  pulling  forwards  on  the  lever  m,  which 
swings  around  the  rod  g.  One  end  of  each  core  is  sup¬ 
ported  in  the  openings  n2  n2 ,  with  the  inner  end  of  which 
they  are  flush.  The  other  ends  have  rods  k  that  slide  in 
brackets  jj  to  make  them  move  in  line.  The  cores  o  are 
moved  in  a  convenient  manner  by  means  of  a  lever  l  fast¬ 
ened  to  a  shaft  g.  When  the  latter  is  turned  by  the  lever 
m,  the  cores  will  move  forwards  until  they  project  into  the 
openings  nx,  occupying  the  positions  indicated  by  the  dotted 
lines,  against  the  stops  p.  The  filling  and  tamping  is  now 
continued  until  the  mold  is  filled.  As  the  top  of  the  mold 
represents  the  back  of  the  finished  block,  this  part  of  the 
block  is,  in  general,  not  given  a  finished  appearance.  All 
that  is  necessary  is  to  level  it  with  an  ordinary  wooden 
float  so  as  to  remove  all  surplus  material. 

The  lever  m  is  now  pushed  backwards  so  as  to  withdraw 
the  cores  from  the  block.  By  swinging  the  cam-levers  ex  and 
e2  upwards,  the  mold  is  released  from  the  plate  b,  and  by 
using  the  levers  as  handles,  the  mold  is  swung  forwards  until 
it  rests  on  the  bracket  i  and  occupies  the  position  indicated  in 
Fig.  12  (6).  The  doors  are  then  let  down,  as  shown,  resting 
on  the  curved  brackets  h,  Fig.  12  (a).  After  the  face  plate  d 
has  been  tilted  away,  the  block  is  free  and  may  be  removed 
on  the  pallet  c. 

It  will  be  noticed  that  the  block,  besides  having  cavities 
b2  and  b2,  has  depressions  a4  in  the  end  surfaces.  These  are 
formed  by  the  projections  a3  in  the  end  doors  ax  and  a2. 


32 


CONCRETE  BUILDING  BLOCKS 


36 


After  inserting  another  pallet  ct  and  swinging  the  mold  into 
its  original  position  the  molding  of  another  block  may  begin. 

54.  If  a  press  is  used,  the  entire  mold  should  be  filled 
before  pressure  is  applied.  The  press  is  designed  to  exert 
sufficient  pressure  to  bring  the  particles  of  the  mass  into 
intimate  contact  and  to  expel  the  air  from  the  block  through 
numerous  vent  holes  provided  in  the  mold.  It  is  customary 
in  pressure  machines  to  have  the  face  on  the  top  of  the  mold 
as  it  is  filled,  so  that  the  application  of  face  matter  involves 
only  striking  out  from  the  top  of  the  mold  \  or  ^  inch  of  the 
coarse  material,  which  is  replaced  by  face  matter  before 
pressure  is  made.  There  are,  however,  as  has  been  described, 
types  of  machines  on  the  market  in  wffiich  the  operation  is 
reversed  and  the  face  matter  deposited  first  in  the  bottom  of 
the  mold,  in  which  case  the  block  is  discharged  with  the 
face  on  the  side. 


FACING  OF  CONCRETE  BLOCKS 

55.  As  provision  must  be  made  for  introducing  face 
matter  at  time  of  filling  the  mold,  it  is  well  to  consider  here 
the  general  subject  of  facing.  As  previously  explained,  in 
a  face-down  machine,  the  face  matter  should  be  deposited 
first;  in  a  side-face  machine,  it  should  be  deposited  by  use  of 
a  thin  partition,  unless  the  mold  is  fitted  with  a  tilting  device 
to  obviate  the  use  of  a  partition;  and  in  a  face-up  machine, 
it  should  be  deposited  last.  There  has  been  a  great  deal  of 
opposition  to  facing  concrete  blocks  with  a  finer  and  richer 
mixture  than  that  used  in  the  body  of  the  block.  This  opposi¬ 
tion  has  been  caused  by  the  belief  that  it  is  impossible  to  put 
on  a  face  that  will  not  crack,  peel,  or  separate  from  the  body 
of  the  block,  this  apprehension  being  based  on  the  difficulty 
of  securing  an  adequate  bond  between  body  and  face,  or  on 
the  unequal  expansion  of  the  differing  mixtures. 

In  practice,  the  theoretical  inequality  of  expansion  has  not 
proved  disastrous,  and  the  securing  of  an  adequate  bond 
between  the  body  and  the  face  is  merely  a  matter  of  method. 
The  essential  points  of  successful  facing  are  two: 


§  30  CONCRETE  BUILDING  BLOCKS  33 

1.  The  face  and  body  of  the  block  must  be  made  at  the 
same  time. 

2.  The  compression  of  material  must  be  so  thorough  that 
the  back  of  the  face  and  the  front  of  the  body  of  the  block  will 
be  mashed  into  each  other,  so  that  there  will  be  no  distinct 
line  where  one  joins  the  other.  Thus  only  may  an  indestruc¬ 
tible  bond  be  secured  between  the  two. 

56.  The  advantages  of  facing  are  four,  namely,  better 
appearance,  waterproofing,  saving  material,  and  greater 
strength. 

The  exterior  appearance  of  a  block  is  improved  by  the  use 
of  a  liner  and  richer  face,  and  this  face  enables  the  manu¬ 
facturer  to  use  plates  of  design  that  would  be  impracticable 
in  a  mixture  of  coarse  concrete.  It  also  enables  him  to  intro¬ 
duce  into  the  face  matter  expensive  colors  that  would  make 
the  cost  prohibitive  if  used  throughout  the  block. 

The  advantage  of  waterproofing  is  considerable.  A  block 
may  be  rendered  nearly  waterproof  by  a  mixture  of  1-2  or 
1-3  cement  and  fine  sand.  This  is  due  to  the  fact  that 
impermeability  is  determined  by  the  size  of  openings  rather 
than  by  the  total  percentage  of  voids. 

The  saving  of  material  where  blocks  must  have  an  exterior 
of  fine  texture  is  enormous,  because  only  £  or  £  inch  of  the 
finer  and  more  expensive  material  is  required. 

Greater  strength  obtains  in  like  cases,  for  it  is  impossible, 
by  the  use  of  any  quantity  of  cement,  short  of  that  which 
would  bankrupt  the  block  maker,  to  secure  in  a  block  manu¬ 
factured  of  fine  sand  the  same  strength  that  is  easily  obtained 
in  a  well-proportioned  1-2-4  or  1-3-5  mixture  containing 
large  aggregate.  Indeed,  a  block  made  entirely  of  face  matter 
could  not  be  properly  called  a  concrete  block. 


211—28 


34 


CONCRETE  BUILDING  BLOCKS 


§3(3 


COMPRESSING  THE  MATERIAL 

57.  Following  immediately  upon  depositing  the  material, 
attention  must  be  given  to  the  proper  condensation  of  the 
material  in  the  mold.  To  obtain  satisfactory  strength, 
density,  and  impermeability  in  the  block,  the  various  particles 
in  the  composition  must  be  . brought  into  such  intimate  con¬ 
tact  that  the  cement  will  be  enabled  to  perform  its  office  as 
an  adhesive  agent,  uniting  the  loose  mass  into  a  firm  unit. 
Attention  has  already  been  called  to  the  importance  of  so 
proportioning  the  materials  that  voids  will  be  eliminated  as 
far  as  possible.  This  elimination  is  necessarily  imperfect 
unless  adequate  care  is  taken  to  condense  the  material  in  such 
a  way  that  the  air  is  expelled  from  it. 

There  are  three  general  methods  of  securing  this  condensa¬ 
tion,  namely,  lamping ,  compressing ,  and  pouring. 

58.  The  more  common  of  the  methods  used  in  general 
concrete  work  is  tamping.  It  was  adopted  by  the  early 
advocates  of  concrete  blocks  as  the  most  readily  apparent 
method.  Thorough  and  conscientious  tamping  will  result 
in  ramming  the  material  to  place  in  a  satisfactory  manner, 
but  it  must  be  observed  that  tamping  should  be  done  in  a 
more  industrious  and  more  intelligent  manner  than  is  common 
in  many  concrete-block  factories.  There  is  also  difficulty  in 
adapting  hand  tamping  to  the  use  of  coarse  material  mixed 
wet,  which  is  now  generally  accepted  as  better  for  block  work 
than  the  dry-sand  mixture  of  the  early  days.  A  compara¬ 
tively  dry  mixture  of  cement  and  sand  will  pack  under  the 
blows  of  a  tamper  in  a  manner  impracticable  in  a  wet  mixture 
or  in  one  containing  a  considerable  portion  of  coarse  aggre¬ 
gate.  In  the  coarse  mixture,  the  blows  of  the  tamper  often 
dislodge  adjoining  portions  of  the  block,  while  in  a  wet  mix¬ 
ture  there  is  always  a  tendency  of  the  concrete  to  squash 
under  the  blows. 

To  overcome  the  labor  incident  to  hand  tamping  and  to 
eliminate  the  personal  factor  so  disastrous  to  uniformity, 
power  tampers  have  been  devised  by  which  the  quality  of  the 


§36 


CONCRETE  BUILDING  BLOCKS 


35 


product  is  vastly  improved.  Of  course,  the  single  pneumatic 
tamper  possesses  no  advantage  over  a  hand  tamper  except 
in  speed,  force,  and  endurance.  To  overcome  the  difficulties 
attendant  upon  using  the  desirable  coarse  aggregate  and  the 
wet  mix,  a  step  further  is  taken  by  introducing  multiple 
tampers,  so  that  the  various  parts  of  the  block  receive  blows 
almost  simultaneously.  This  is  a  comparatively  new  depar¬ 
ture,  but  the  principle  seems  to  be  substantially  correct. 

59.  Compressing. — With  the  introduction  of  coarse 
aggregate  and  medium-wet  mixtures,  compressing  by 
means  of  mechanical  and  hydraulic  presses  came  into  use. 
The  aim  of  these  presses  is  to  overcome  the  personal  equation 
by  providing  a  machine  that  will  do  uniform  and  effective 
work.  As  previously  stated,  the  mold  is  filled  and  only  one 
pressure  is  made  on  the  entire  block.  The  mechanical  presses 
are  usually  rated  to  give  each  block  a  pressure  of  50  tons, 
which  is  considered  ample  for  the  compression  of  an  ordinary 
block.  Vent  holes  are  provided  for  the  expulsion  of  air, 
and  these  should  never  be  allowed  to  close.  The  hydraulic 
presses  commonly  used  give  an  ultimate  pressure  up  to 
200  tons,  but  they  are  slower  in  action  than  mechanical 
presses,  because  of  the  time  consumed  in  pumping  up  the 
cylinders.  This  lack  of  speed  in  operation  is  overcome  by 
molding  several  blocks  at  one  time,  as  the  pressure  can  be 
obtained  much  greater  than  necessary  for  a  single  block. 

60.  Pouring.  —  In  the  condensation  method  known  as 
pouring,  a  fluid  mixture  is  poured  into  molds  and  allowed 
to  attain  a  minimum  volume  by  gravity.  There  are  serious 
objections  to  pouring,  both  from  a  technical  and  a  practical 
standpoint.  As  to  the  former,  it  is  evident  that  the  cement, 
being  heavier,  sinks  to  the  bottom  and  that  the  block,  there¬ 
fore,  is  not  of  uniform  strength.  As  to  the  latter,  the  time 
necessary  to  leave  the  block  in  the  mold  necessitates  tying  up 
a  large  sum  in  equipment.  The  pouring  process,  however, 
has  its  good  points,-  and  it  is  particularly  efficacious  in  the 
production  of  members  that  are  to  be  especially  ornamented. 


36 


CONCRETE  BUILDING  BLOCKS 


§36 


These  members  are  usually  manufactured  either  in  sand 
molds  or  in  plaster  molds,  in  which  glue  negatives  are  used  if 
there  is  to  be  an  undercut  in  the  ornamental  parts. 


OFF-BEARING  AND  CURING 

61.  Off-Bearing. — The  delivery  of  a  block  and  its 
off-bearing  may  seem  to  be  matters  that  are  too  trivial  to 
deserve  special  mention ;  yet  it  is  in  the  careless  removal  from 
the  mold  that  corners  are  knocked  off,  that  patches  are  pulled 
from  the  face,  and  that  various  irreparable  injuries  are  done 
to  the  block.  Care  and  a  desire  for  perfect  work,  rather  than 
haste  in  manufacture,  are  factors  that  will  help  to  prevent 
such  injuries.  But  there  are  two  other  points  that  bear 
vitally  on  this  stage  of  the  manufacturing  process.  One  is 
the  use  of  a  mixture  adapted  to  give  best  results  in  the  par¬ 
ticular  machine  used,  and  the  other  is  the  care  of  machinery. 
There  are  very  few  plants  in  which  the  machinery  is  carefully 
cleaned  and  oiled  at  the  close  of  the  day’s  work,  and  yet  these 
are  some  of  the  most  essential  factors  of  success.  Not  much 
time  is  required  in  cleaning  and  oiling,  and  if  the  work  is  care¬ 
fully  done,  a  much  better  and  a  much  larger  product  will 
result  than  if  the  machinery  is  neglected. 

Very  many  blocks  have  incipient  cracks  started  while  being 
carried  from  the  machine  to  the  car  on  which  they  are  to 
cure.  The  off-bearer  may  be  careless,  but  more  often  he 
is  required  to  carry  a  block  whose  weight,  while  not  heavy 
in  an  ordinary  sense,  is  too  great  to  be  handled  with  the  care 
due  a  freshly  made  block.  The  point  to  bear  in  mind  is  the 
extreme  sensitiveness  of  freshly  molded  concrete  and  the 
necessity  of  adapting  the  discharge  and  handling  to  this 
sensitiveness,  so  that  the  block  will  not  be  deformed  in  any 
way  before  the  initial  set. 

62.  Curing. — By  curing. is  meant  more  than  aging, 
and  something  that  is  entirely  different  from  drying.  The 
curing  period  is  the  critical  stage  of  transformation  in  which 
a  mass  of  cement,  sand,  gravel,  and  water  becomes  a  hard, 


§36 


CONCRETE  BUILDING  BLOCKS 


37 


dense,  and  enduring  unit  suitable  for  building  purposes. 
The  essential  element  in  curing  is  moisture,  but  its  applica¬ 
tion  is  governed  by  certain  conditions  that  must  be  diligently 
observed. 

The  first  condition  that  the  moisture  used  in  curing  must 
comply  with  is  that  it  shall  be  sufficient  as  to  quantity.  The 
block  must  be  kept  thoroughly  wet  in  order  to  secure  that 
thorough  crystallization  essential  to  ultimate  strength. 

The  second  condition  is  uniformity  in  applying  the  mois¬ 
ture.  The  block  must  be  kept  uniformly  damp  in  every  part 
and  at  all  times.  This  involves  sprinkling  so  frequently  that 
the  edges  or  corners  of  the  block  will  not  become  partly  dry. 
No  set  rule  that  will  govern  all  conditions  of  climate  and  tem¬ 
perature  can  be  given.  The  hotter  and  dryer  it  is,  the  more 
frequent  must  be  the  sprinkling.  Three  times  a  day  should 
be  the  minimum. 

The  third  condition  is  that  the  duration  of  the  curing 
process  shall  be  sufficient.  The  sprinkling  should  begin  as 
early  as  possible  without  marring  the  block.  The  duration 
of  the  sprinkling  period  depends  on  the  consistency  of  mix¬ 
ture  used.  It  should  never  be  less  than  1  week,  and  from 
that  to  2  weeks.  After  the  sprinkling  has  ceased,  the  block 
should  be  exposed  to  the  atmosphere  and  allowed  to  age 
1  or  2  weeks  longer  before  going  into  a  building. 

The  fourth  condition  is  that  the  method  of  application  shall 
be  a  suitable  one.  The  water  should  be  sprinkled,  preferably 
by  spray  from  a  hose  nozzle.  In  larger  plants,  the  introduc¬ 
tion  of  pipes  fixed  over  the  blocks  will  eliminate  the  expense 
of  a  hose  tender.  The  best  practice  is  to  cover  the  blocks 
with  some  material  that  will  serve  in  a  measure  to  retain 
moisture.  Clean  hay,  straw,  or  burlap  will  answer.  Any  of 
these  materials  will  add  greatly  to  the  maintenance  of  a 
uniform  condition  of  moisture  in  the  air  immediately  sur¬ 
rounding  the  blocks. 

The  fifth  condition  is  the  provision  of  climatic  protection. 
The  blocks  as  they  come  from  the  mold  should  be  placed  on 
racks  or  cars  and  allowed  to  remain  there  for  36  or  48  hours, 
when  they  will  be  hard  enough  to  stack.  In  stacking,  no 


38 


CONCRETE  BUILDING  BLOCKS 


§36 


block  should  come  in  contact  with  another.  This  may  be 
arranged  by  placing  lath  between  them,  the  idea  being  to 
prevent  discoloration  by  contact  and  to  insure  a  free  cir¬ 
culation  of  air  on  all  sides  of  each  block.  It  is  absolutely 
necessary  to  protect  the  blocks  from  both  wind  and  sun 
during  the  sprinkling  period.  In  general,  the  whole  idea  of 
curing  may  be  summed  up  in  one  word — uniformity. 
Exposure  to  wind  and  sun  will  ruin  the  appearance  and 
impair  the  strength.  Consequently,  ample  curing  sheds 
must  be  provided  to  care  for  blocks  until  they  cease  to  require 
sprinkling. 

63.  The  curing  of  blocks  in  winter  has  presented  a  prob¬ 
lem  so  serious  that  many  plants  have  ceased  to  operate  during 
cold  weather.  This,  however,  is  unnecessary.  The  most 
simple  means  of  securing  a  satisfactory  cure  in  winter  is  by 
encasing  the  curing  shed  with  side  walls  built  of  blocks  and 
heating  it  by  large  stoves.  This  plan  has  proved  entirely 
satisfactory. 

Perhaps  the  problem  of  winter  work,  more  than  anything 
else,  has  prompted  the  introduction  of  steam  curing  rooms, 
although  the  practice  of  the  sand-lime  brick  industry  in  this 
regard  has  undoubtedly  had  its  influence  on  block  makers’ 
methods.  Steam  curing  differs  in  some  important  essentials 
from  the  curing  process  already  described.  It  involves  the 
building  of  a  series  of  steam  rooms,  with  walls  of  blocks,  floors 
of  concrete,  and  a  roof  preferably  of  the  same  material.  As 
the  blocks  come  from  the  mold  they  are  loaded  on  cars,  and 
each  car,  when  full,  is  run  into  a  steam  room.  When  the 
room  is  full,  the  doors  are  not  closed,  but  are  allowed  to 
remain  open  for  24  hours  while  the  steam  valve  in  the  room 
is  opened  barely  enough  to  moisten  the  atmosphere  by  esca¬ 
ping  steam.  At  the  end  of  24  hours,  the  doors  are  closed  and. 
the  carloads  of  blocks  are  steamed  for  36  hours,  exhaust  steam 
being  used  in  the  daytime  and  a  low  pressure  live  steam  at 
night.  At  the  end  of  36  hours’  steaming,  the  cars  are  run 
into  a  yard  where  the  blocks  are  stacked  and  protected  from 
sun  and  wind  for  48  hours,  during  which  period  they  are  sub- 


§  36 


CONCRETE  BUILDING  BLOCKS 


39 


jected  to  sprinkling.  Curing  by  this  method  shows  results 
equal  to  10  days  by  sprinkling,  and  the  blocks  are  consider¬ 
ably  lighter  in  color.  It  is  apparent  that  a  series  of  rooms  is 
needed  to  render  the  process  continuous.  Steam  curing  not 
only  facilitates  winter  work,  but  effects  a  great  saving  of  shed 
room  because  of  the  shorter  time  required  to  protect  the  blocks. 
This  method  of  curing  of  course  entails  some  initial  expen¬ 
diture,  but  it  seems  to  be  the  method  of  the  future. 


ARRANGEMENT  AND  EQUIPMENT  OF  FACTORY 


SELECTION  OF  BLOCK  MACHINE 

64.  In  considering  the  selection  and  arrangement  of 
equipment  for  a  concrete-block  plant,  the  block  machine  is 
generally  regarded  as  not  merely  the  essential  feature,  but  as 
the  only  portion  of  the  equipment  worthy  of  study.  While 
admitting  the  importance  of  using  care  in  selecting  a  block 
machine,  it  will  be  shown  that  other  equipment  and  other 
considerations  also  make  vitally  for  success  or  failure  in  the 
plants  of  the  day. 

65.  In  selecting  a  machine,  it  is  well  to  analyze  the 
results  that  it  is  possible  for  a  machine  to  effect,  to  formulate 
the  purposes  for  which  a  machine  is  desired,  and  to  weigh 
the  properties  of  each  particular  machine  for  these  purposes. 
In  this  way,  a  machine  may  be  selected  that  will  serve  one’s 
particular  purpose  more  perfectly  than  can  be  hoped  if  a 
selection  is  made  in  a  haphazard  manner  without  analysis 
and  comparison. 

The  chief  points  by  which  to  judge  a  block  machine  are  as 
follows:  (1)  The  form  of  the  block;  (2)  the  adjustability  as 
to  size;  (3)  the  variation  as  to  shape;  (4)  the  design  of  the 
face  plates;  (5)  the  facility  in  filling;  (6)  the  ease  of  condensa¬ 
tion  ;  (7)  the  adaptability  to  the  use  of  wet  material ;  (8)  the 
provisions  for  facing;  (9)  the  perfection  of  discharge;  and 
(10)  the  general  rapidity. 


40 


CONCRETE  BUILDING  BLOCKS 


§36 


It  is  not  the  purpose  to  give  a  number  of  illustrations  of 
various  machines  nor  to  describe  in  detail  the  mechanism 
or  operation  of  any  particular  machine,  for  the  reason  that 
such  information  may  be  derived  from  the  catalogs  of  the 
manufacturers. 

66.  Form  of  Block. — First  of  all,  the  machine  must 
be  selected  with  reference  to  the  form  of  block  and  the  style 
of  wall  considered  best. 

There  are  many  machines  that  make  the  one-piece  blocks 
already  described,  but  the  form  varies  as  the  machines  intro¬ 
duce  one,  two,  or  three  interior  cores,  each  of  which  creates  a 
perpendicular  air  space.  In  general,  this  type  is  known  as  the 
hollow  block. 

The  staggered  air-space  block,  shown  in  Fig.  11,  has  two 
rows  of  air  spaces,  the  air  space  in  one  row  backing  the  web 
in  the  other  and  producing  the  zigzag  effect  implied  by  its 
name.  Consequently,  no  web,  or  partition,  passes  directly 
from  the  face  section  to  the  back,  but  each  takes  a  roundabout 
way,  the  intention  being  to  make  more  devious  the  route 
that  the  water  must  travel. 

The  blocks  that  consist  of  two  slabs  united  by  metal  ties 
go  still  further  by  removing  the  middle  portion  and  using 
metal  rods  in  its  place,  thus  giving  a  clear  air  space  in  the  wall. 

67.  Adjustability  as  to  Size. — The  adjustability  as 
to  size  is  one  of  the  most  important  items  to  consider  in 
selecting  a  block  machine.  As  to  the  thickness  of  the  wall, 
this  adjustability  must  cover  the  range  from  the  thinnest 
partition  wall  to  a  wall  as  wide  as  may  be  required  in  any 
building.  There  must  be  reasonable  adjustment  as  to  the 
height  of  courses,  in  order  to  secure  the  pleasing  effect  of  an 
alternation  of  wide  and  narrow  courses  in  a  wall,  as  well  as  to 
provide  for  a  course  of  Unusual  height  when  demanded  in 
building  construction.  There  must  also  be  adjustability  as  to 
length  of  blocks,  in  order  to  bring  an  opening  for  a  window 
or  a  door  at  a  particular  place.  The  time  has  passed  when 
the  plan  of  a  house  may  be  changed  to  fit  the  blocks.  The 
blocks  must  be  made  to  fit  the  plans. 


§36 


CONCRETE  BUILDING  BLOCKS 


41 


68.  Variation  as  to  Shape. — It  must  be  possible  to 
make  wide  variation  as  to  shape,  involving  first  the  stringer, 
or  main  wall,  block,  then  the  various  fractional  blocks,  and 
finally  different  styles  of  blocks  for  the  various  jambs.  There 
will  also  have  to  be  made  a  strong  and  substantial  corner  block 
that  will  preserve  the  general  plan  of  bonding  the  wall.  If  to 
these  may  be  added  blocks  for  bay-window  angles,  as  well  as 
blocks  for  circles,  arches,  keystones,  and  the  like,  it  will  give 
the  manufacturer  a  feeling  of  confidence  to  undertake  con¬ 
struction  that  he  could  not  attempt  with  a  machine  of  limited 
adjustability. 

69.  Design  of  Face  Plates. — The  design  of  face  plates 
is  a  very  important  consideration,  both  as  to  number  and 
quality.  Some  plates  are  stamped  from  metal  and  others  are 
cast.  Cast-metal  plates  are  considered  superior  to  stamped- 
metal  plates,  because  the  lines  produced  by  the  latter  are 
indistinct.  There  is  a  wide  range  for  selection,  and  some 
manufacturers  offer  a  great  number  of  designs.  The  best 
practice  would  seem  to  be  to  select  plates  that  display  some 
artistic  skill.  The  rock  face  has  been  so  popular  that  often 
a  building  has  been  constructed  in  which  all  the  blocks  present 
the  same  design  of  rock  facing.  It  is  clear  that  to  secure  any 
natural  effect  in  rock-face  work  one  must  have  a  considerable 
variety  of  plates.  The  rock  face  is  not  only  the  more  common 
face  in  general  use,  but  is  in  greater  danger  of  abuse  by  the 
unskilled.  The  making  of  an  entire  building  of  rock-face 
blocks  should  be  the  exception,  rather  than  the  rule.  The 
bevel-edge  and  tooled-face  designs,  as  well  as  the  perfectly 
plain,  smooth  face,  present  a  rich  appearance,  and,  when 
relieved  by  a  suitable  cornice,  water-table,  and  rock-face 
basement,  they  give  to  residences  a  very  handsome  exterior. 

70.  Facility  of  Filling. — The  facility  of  filling  depends 
largely  on  the  hopper  used  and  on  the  arrangement  of  the 
cores  in  the  mold.  A  very  thin-faced  section,  or  back,  or 
cores  very  close  together  will  naturally  render  filling  difficult 
and  the  operation  slower,  will  require  greater  care  in  making 
and  handling  the  blocks  and  preclude  the  possibility  of  employ- 


42 


CONCRETE  BUILDING  BLOCKS 


§36 


ing  coarse  aggregate.  This  last  consideration  is  perhaps 
the  most  important  one  in  reference  to  ease  of  filling.  A 
machine  should  provide  in  every  section  of  the  mold  space 
sufficient  for  the  working  of  coarse  aggregate  without  clogging. 

71.  Ease  of  Condensation. — The  ease  with  which  con¬ 
densation  may  be  effected  is  naturally  governed  by  the  process 
in  use;  whether  tamping,  compressing,  or  pouring.  In  the 
case  of  tamping,  if  done  by  hand,  the  thoroughness  of  the 
process  depends  entirely  on  the  integrity  and  endurance  of  the 
workman.  If  condensation  is  attained  by  compression,  it  is 
a  matter  of  adjustment  of  machinery.  In  the  pouring  process 
it  depends  on  the  amount  of  water  used.  In  the  case  of 
any  of  these  methods,  it  is  necessary  to  see  that  the  machine 
chosen  is  perfectly  adapted  to  condense  the  concrete  in  an 
efficient  manner. 

72.  Adaptability  to  Use  of  Wet  Material. — In  the 
early  days  of  the  concrete-block  industry  many  machines  were 
specially  adapted  to  the  use  of  a  dry  mix,  and  in  a  national 
convention  of  a  few  years  ago  the  advocates  of  a  medium-wet 
mix  were  distinctly  in  the  minority.  However,  conditions 
are  different  now,  and  many  concrete-block  makers  recog¬ 
nize  a  necessity  of  adhering  to  rules  governing  concrete 
construction  in  general.  The  danger,  therefore,  now  lies 
in  unscrupulous  machinery  manufacturers  advertising  that 
their  machines  are  adapted  to  the  use  of  a  wet  mixture, 
whereas  they  may  be  worked  to  their  greatest  capacity  only 
with  dry  material.  The  question  of  the  amount  of  moisture 
in  the  mix  goes  to  the  very  core  of  the  whole  subject.  It 
depends  on  the  general  process  of  manufacture  and  the 
devices  used  in  connection  with  filling  the  mold  and  dischar¬ 
ging  the  material,  and  is  a  matter  of  vital  interest  bearing 
directly  on  the  quality  of  the  finished  product. 

In  connection  with  the  discharge  of  blocks,  it  is  necessary 
to  investigate  the  kind,  the  cost,  and  the  number  of  pallets, 
or  bottom  plates,  on  which  the  blocks  are  carried  away  after 
molding.  The  pallets  vary  from  pine  boards  to  iron  plates, 
and  it  is  worth  while  to  find  out  whether  one  size  will  answer 


§  36 


CONCRETE  BUILDING  BLOCKS 


43 


for  all  different  blocks  or  whether  the  particular  machine 
will  require  several  lots  of  pallets  for  different  sizes  of  blocks 
and  different  widths  of  walls. 

73.  Provisions  for  Facing. — The  facility  with  which 
a  block  may  be  faced  is  also  a  matter  that  should  be  looked 
into.  As  has  been  noted,  there  are  face-down,  face-up,  and 
side-face  machines.  The  latter  type  is  often  supplemented 
by  some  device  for  tilting  the  mold  or  otherwise  rendering 
facing  more  easy.  The  points  to  be  borne  in  mind  in  this 
particular  are  as  follows:  (1)  The  machine  should  admit 
of  facing  without  unnecessary  loss  of  time,  and  (2)  it  should 
admit  of  such  methods  that  an  indestructible  and  absolutely 
permanent  bond  will  obtain  between  the  body  and  the  face 
of  the  block. 

74.  Perfection  of  Discharge. —  Another  point  of 
considerable  importance  in  the  selection  of  a  machine  is  the 
facility  with  which  the  blocks  can  be  withdrawn  from  the 
mold.  Care  must  be  taken  not  to  buy  a  machine  that  is 
apt  to  offer  difficulties  in  withdrawing  the  blocks  without 
breakage. 

75.  General  Rapidity. — Referring  to  the  general  rapid¬ 
ity  of  manufacture,  it  is  necessary  to  be  able  to  supply  a 
large  demand  without  using  so  large  a  number  of  machines 
that  the  investment  renders  the  business  unprofitable.  Also, 
it  is  necessary  to  secure  from  a  given  number  of  men  an 
output  that  will  bring  profit  from  their  labor  and  at  the 
same  time  enable  the  manufacturer  to  compete  with  other 
building  materials  common  in  his  locality. 

The  rapidity  of  a  particular  machine  depends  on  the 
mechanical  details  of  operation  that  have  been  incorporated 
into  the  machine  and  on  the  training  of  the  men.  The 
machine  selected  must  be  perfect  in  those  almost  insignificant 
labor-saving  devices  that,  in  the  end,  will  augment  the  daily 
output  without  any  loss  of  quality  in  the  block. 


44 


CONCRETE  BUILDING  BLOCKS 


§36 


SELECTION  OF  MIXER 

76.  There  are  two  general  types  of  batch  mixer.  One 
agitates  the  mass  by  means  of  interior  blades,  or  deflectors, 
and  the  other  secures  a  similar  result  by  the  shape  of  the 
receptacle  in  which  the  material  is  revolved.  The  choice 
between  these  two  types  depends  on  the  character  of  the 
material  used  and  the  consistency  of  the  mix.  Both  types 
are  being  satisfactorily  employed  in  block  plants.  Continu¬ 
ous  mixers  are  also  often  used  and  if  the  ingredients  are 
properly  fed  to  the  mixer  they  form  an  efficient  machine. 


ARRANGEMENT  OF  MACHINERY 

77.  The  location  of  the  mixer  is  a  matter  of  great  moment 
to  the  block  maker.  Wherever  possible,  this  machine  should 
be  located  above  the  block  machine,  so  that  the  mixed  material 
can  be  discharged  on  a  mixture  table,  from  which  it  can  be 
raked  directly  into  the  mold.  The  location  of  the  mixer  in 
this  position  naturally  involves  a  still  greater  elevation  of 
sand,  gravel,  stone,  cement,  etc.  In  the  better  arranged 
plants,  cement-storage  bins  are  located  in  the  upper  part  of 
the  building,  and  a  belt  conveyer  is  used  to  unload  the  sacked 
cement  from  cars.  In  the  upper  part  of  the  building  also 
may  be  located  all  the  screens  and  other  accessories  that  are 
brought  into  use  in  preparing  material  for  the  mixer.  The 
sand,  as  well  as  the  coarse  aggregate,  can  be  brought  up  as 
required  by  an  enclosed  bucket  conveyer  located  just  outside 
the  building  and  discharging  into  a  chute,  which  feeds  the 
material  to  the  screens.  After  leaving  the  screens  the 
material,  with  the  proper  proportion  of  cement  added,  is 
shoveled  into  a  hopper  holding  one  charge  for  the  mixer,  and 
this  material,  in  turn,  is  controlled  by  a  shut-off  operated  from 
below  by  the  man  at  the  mixer.  It  is  contemplated  that 
water  will  be  piped  to  the  mixer  from  either  the  city  main  or 
a  private  overhead  tank,  and  that  an  automatic  measuring 
device  will  be  used  to  secure  a  uniform  quantity  of  water  in 
each  batch. 


§36 


CONCRETE  BUILDING  BLOCKS 


45 


The  arrangement  just  outlined  requires  a  somewhat  exten¬ 
sive  building.  If  such  a  building  cannot  be  procured,  and  it 
is  necessary  to  have  all  equipment  on  the  same  level,  the 
transference  of  material  between  the  different  stages  of  the 
process  may  be  accomplished  by  introducing  belt  conveyers. 
It  is  especially  advisable,  however,  to  raise  the  material  from 
the  mixer  to  the  mixture  table  or  the  hopper  of  the  block 
machine  in  the  manner  just  described,  as  shoveling  the 
material  up  by  hand  is  unsatisfactory  and  expensive. 

78.  In  very  small  plants,  stationary  racks  serve  to  hold 
blocks  during  the  first  period  of  the  curing  process,  but  in  an 
establishment  designed  to  turn  out  large  quantities  of  blocks, 
it  is  as  essential  to  have  the  racks  mounted  on  cars  as  it  is  to 
have  a  block  machine.  Steel  cars  specially  designed  for  the 
purpose  may  be  procured  at  reasonable  prices.  Such  cars  are 
usually  more  satisfactory  than  cars  made  of  2-inch  lumber 
mounted  on  metal  trucks.  However,  such  trucks  may  be 
procured  very  cheaply  if  the  manufacturer  prefers  to  build 
his  own  cars  from  lumber. 

Experience  has  proved  wooden  car  tracks  to  be  unsatis¬ 
factory,  and  a  light  T  rail  should  therefore  be  used.  The 
tracks  should  be  arranged  systematically,  with  switches  or 
transfer  tables,  so  that  a  car  when  loading  may  be  very  close 
to  the  machine  and  may  afterwards  be  pushed  to  any  desired 
point  in  the  curing  shed  or  steam  room. 

79.  The  best  appliance  for  sprinkling  blocks  is  an  over¬ 
head  water  pipe,  with  branches  extending  through  the  curing 
shed  and  equipped  with  inverted  lawn  sprinklers  at  such 
distances  that  each  car  or  stack  of  blocks  can  be  readily 
sprinkled  by  turning  on  the  water  in  a  particular  branch  of 
the  pipe.  In  this  way,  the  use  of  the  hose  can  be  almost 
entirely  eliminated. 

Assuming  that  steam  curing  is  not  employed,  some  provision 
must  be  made  for  a  warm  room  in  which  to  cure  blocks  in 
winter,  as  well  as  artificial  heat  in  that  section  of  the  plant 
where  the  machine  is  located.  It  is  also  advantageous  to 
locate  the  sand  bins  so  that  some  warmth  will  reach  them. 


46 


CONCRETE  BUILDING  BLOCKS 


§36 


In  view  of  the  heat  required  in  winter,  it  is  much  better  to 
equip  a  plant  with  a  steam  boiler.  Lacking  steam,  however, 

resort  must  be  made  to  stoves.  These  must  be  looked  after 

/ 

diligently  enough  to  maintain  uniform  temperature  in  the 
curing  room  during  the  severest  weather.  The  steam  room, 
however,  is  the  easiest  solution  of  this  problem  as  well  as 
many  others. 


SELECTION  OF  WORKMEN 

80.  After  the  plant  equipment  has  been  selected  and 
arranged  with  a  view  to  securing  the  best  results,  there  still 
remains  a  vital  factor  to  be  considered.  This  factor  is  the 
personal  intelligence,  energy,  and  integrity  of  each  man 
employed  about  the  plant,  and  is  one  that  is  sometimes 
entirely  overlooked  or  underrated  in  its  importance. 

There  must  be  a  foreman  who  is  thoroughly  conversant  with 
the  uses  of  cement.  On  his  knowledge  depends  the  constant 
inspection  of  material,  the  proper  proportioning  of  the  various 
ingredients  of  the  block,  the  consistency  of  the  mix,  and  the 
correctness  of  mixing,  manufacturing,  and  curing.  Further 
than  this,  the  foreman  must  be  a  man  of  such  experience  in 
structural  work  that  he  can  take  the  architect’s  blueprints 
and  make  blocks  that  will  fit  without  cutting  or  filling. 
Given  such  a  foreman,  the  men  in  each  branch  of  the  work 
will,  if  of  ordinary  intelligence  and  character,  rapidly  absorb 
enough  of  his  spirit  to  do  their  own  part  of  the  work  thor¬ 
oughly  well.  It  is  a  fatal  mistake  to  employ  the  cheaper  class 
of  ignorant  labor  in  a  concrete-block  plant  because  the  manu¬ 
facture  of  concrete  blocks  is  a  business  that,  in  the  final 
summing  up,  depends  on  the  ability  and  conscientiousness  of 
the  block  maker.  An  entire  absence  of  intelligence  cannot 
be  sufficiently  overcome  by  rigid  supervision,  no  matter  how 
effective  the  latter  may  be  for  securing  profitable  results. 


A 


CONCRETE  BUILDING  BLOCKS 

(PART  2) 


DETAILS  OF  THE  USE  AND  PRODUCTION 
OF  CONCRETE  BLOCKS 


DETAILS  OF  MAKING  AND  LAYING 


FOOTINGS  AND  FOUNDATIONS 

1.  The  foundation  of  concrete-block  buildings  requires  as 
much  care  in  its  construction  as  the  foundation  of  a  building 
of  any  other  material. 

If  the  foundation  should  fail,  the  blocks  would  break, 
developing  a  crack  in  the  wall.  To  expect  the  superstructure 
to  remain  intact  without  adequate  attention  to  the  foundation 
is  folly.  The  rules  governing  foundations  of  concrete-block 
buildings  are  not  essentially  different  from  those  governing  in 
any  other  construction  in  which  walls  of  equal  weight  are 
designed  to  carry  similarly  loaded  floors.  The  best  practice 
is  to  figure  the  floor  load  and  weight  of  walls  and  roof  with 
reference  to  the  resistance  of  the  soil  at  the  bottom  of  the 
excavation  and  to  put  in  concrete  footings  accordingly. 
These  footings  must  be  of  a  width  that  will  allow  the  required 
factor  of  safety,  and  must  be  thick  enough  to  distribute  the 
load  without  liability  of  breaking  the  footing.  Upon  this  foot¬ 
ing  should  be  laid  a  basement  wall,  or  foundation,  consisting 
of  blocks.  It  is  unnecessary  to  make  the  foundation,  or  base¬ 
ment,  wall  solid,  because  a  hollow  wall  is  especially  advan- 

COPYRIOHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS*  HALL.  LONDON 

§  37 


CONCRETE  BUILDING  BLOCKS 


§37 


2 

tageous  from  a  sanitary  standpoint  and  may  be  made  amply 
strong  for  foundations  by  employing  a  width  greater  than  that 
used  for  the  superstructure.  If,  in  buildings  designed  to  carry 
heavily  loaded  floors,  the  use  for  which  the  basement  is 
intended  does  not  permit  of  bearing  partitions,  concrete  piers 
should  be  provided  at  suitable  intervals  to  support  the  girders. 


LAYING  AND  FITTING  OF  CONCRETE  BLOCKS 

2.  There  is  scarcely  any  danger  of  placing  too  great 
emphasis  on  the  mason’s  part  in  concrete-block  construction. 
The  proper  placing  of  concrete  blocks  in  a  wall  is  a  factor  that 
determines  the  ultimate  efficiency  of  this  class  of  construc¬ 
tion — a  factor  whose  neglect  operates  to  vitiate  every  good 
quality  of  well-made  blocks. 

3.  Mortar  Joints. — The  first  point  to  be  observed  in 
the  laying  of  concrete  blocks  is  uniformity  in  mortar  joints. 
Very  many  concrete-block  buildings  upon  close  inspection 
show  joints  varying  from  less  than  \  inch  to  more  than  £  inch. 

Tor  such  variations  there  is  no  valid  excuse,  and  it  is  a  prac¬ 
tice  that  is  not  only  detrimental  to  the  strength  and  durability 
of  a  wall,  but  to  the  appearance  of  the  building,  as  well. 
Machinery  manufacturers  have  found  it  impracticable  to 
leave  the  thickness  of  joints  to  the  judgment  of  individual 
masons;  therefore,  in  designing  concrete  block  machines  due 
allowance  is  commonly  made  for  a  constant  size  of  mortar 
joint.  Although  this  varies  in  the  different  makes  of  machines, 
f  inch  seems  to  be  the  happy  medium,  and  this  thickness  is 
approved  as  offering  a  joint  sufficiently  narrow  to  afford  good 
construction  and  pleasing  appearance.  At  the  same  time, 
this  joint  is  wide  enough  to  save  the  mason  needless  trouble 
in  maintaining  it  uniformly  throughout  the  wall. 

Unless  a  non-staining  cement  is  used,  care  must  be  taken 
not  to  let  any  mortar  run  down  on  the  face  of  the  wall.  The 
pointing  as  well  as  the  coloring  of  mortar  joints  is  purely  a 
matter  of  artistic  taste  in  exterior  finish. 


§37 


CONCRETE  BUILDING  BLOCKS 


3 


4.  Composition  of  Mortar* — As  to  the  composition 
of  mortar  to  be  used  in  laying  blocks,  it  is  a  very  serious 
error  to  use  ordinary  lime  mortar  so  commonly  employed 
in  bricklaying.  A  serviceable  mortar  is  composed  of  1  part 
of  cement  and  3  parts  of  sand,  but  as  this  mixture  is  some¬ 
what  difficult  to  work  on  upright  joints,  it  is  now  common 
to  add  a  certain  portion  of  thoroughly  slaked  lime  or  of  the 
commercial  hydrated  lime  to  the  cement  mortar.  If  this 
plan  is  adopted,  a  mortar  consisting  of  1  part  of  cement, 
1  part  of  lime,  and  3  parts  of  sand  will  prove  satisfactory. 
A  thoroughly  reliable  water-proofing  compound  is  a  valuable 
addition  to  mortar  for  laying  concrete  blocks,  as  it  will  pre¬ 
vent  rain  from  penetrating  a  wall  at  the  mortar  joints.  Very 
frequently,  the  concrete  blocks  are  blamed  for  collecting 
moisture  when  the  fault  is  in  the  composition  of  the  mortar 
or  the  method  of  laying. 

5.  Bond. — It  is  important  that  there  should  be  a  firm 
bond  between  the  blocks  and  the  mortar.  Although  the 
mortar  used  in  a  concrete-block  wall  serves  primarily  as  a  bed 
for  the  blocks,  the  intention  is  that  the  adhesion  between  the 
mortar  and  the  blocks  shall  be  so  great  that  the  wall  will  be 
almost  monolithic.  Every  person  versed  in  general  concrete 
construction  recognizes  the  difficulty  of  securing  such 
adhesion  between  a  dry  and  thoroughly  cured  stratum  of 
concrete  and  a  layer  subsequently  deposited.  To  overcome 
this  difficulty,  the  blocks  should  be  immersed  in  water  imme¬ 
diately  before  laying,  so  that  they  will  be  thoroughly  wet 
when  placed  in  the  wall.  Otherwise,  the  dry  surface  of  the 
block  will  absorb  the  water  from  the  mortar  and  the  result 
will  be  “dead”  mortar  in  which  the  cement  is  only  partly 
crystallized,  forming  a  joint  that  is  weak  and  easily  penetrated 
by  water. 

6.  Fitting  of  Blocks. — An  important  point  in  con¬ 
crete-block  construction  is  to  use  blocks  that  have  been 
molded  to  fit  in  their  destined  places.  The  adjustability  of 
the  machine  or  the  ingenuity  of  the  foreman  in  constructing 
special  forms  should  accomplish  this  in  molding,  but  if  it  is 

211—24 


4 


CONCRETE  BUILDING  BLOCKS 


37 


not  so  done,  or  if  there  are  only  a  few  blocks  of  a  special  size 
required,  they  can  be  produced  by  cutting  the  freshly  made 
blocks  with  a  large  knife.  To  cut  blocks  to  fit  on  the  job  is 
possible,  but  it  is  a  practice  that  should  not  be  followed.  It 
not  only  wastes  blocks  and  takes  too  much  of  the  mason’s 
time,  but  results  in  a  careless  method  of  filling  in  pieces  that 
fit  more  or  less  perfectly,  but  never  so  well  as  a  block  made 
for  the  place. 


WALL  CONSTRUCTION 

7.  Width  of  Walls. — The  width  of  concrete-block 
walls  is  often  governed  by  local  civic  regulations,  it  being  com¬ 
mon  to  require  the  same  width  as  is  customary  in  constructing 
solid  brick  walls.  If  there  are  no  regulations  of  this  kind  to 
follow,  it  will  be  safe  to  use  an  8-inch  wall  for  one-story  con¬ 
struction  and  a  10-inch  wall  for  two-story  construction.  For 
a  three-story  building,  the  first  and  second  stories  should 
be  12  inches  wide  and  the  third  10  inches.  For  four-story 
construction,  the  first  and  second  stories  should  be  15  inches 
wide,  the  third  12  inches,  and  the  fourth  10  inches.  The 
basement  walls  should,  in  each  case,  be  from  3  to  5  inches 
wider  than  the  walls  of  first  story. 

8.  Supporting  of  Floor  Joists. —  The  early  practice 
in  reference  to  the  placing  of  floor  joists  in  concrete-block 
structures  was  to  insert  the  ends  in  the  wall,  supporting  them 
either  upon  blocks  having  a  face  section  of  extra  thickness  or 
upon  a  metal  plate  that  distributed  the  load  on  the  under 
course.  The  later  practice,  however,  is  to  employ  steel 
stirrups,  or  joist  hangers,  by  means  of  which  the  joist  is  hung 
inside  of  the  wall.  An  example  of  a  steel  stirrup  is  shown  in 
Fig.  1.  The  part  a  hanging  inside  the  wall  supports  the  joist, 
and  the  parts  h  rest  on  top  of  the  block.  This  method  of  sup¬ 
porting  girders  is  undoubtedly  the  best,  because  the  wall  is 
relieved  from  danger  in  case  of  failure  of  floors  from  over¬ 
loading  or  from  an  interior  fire.  Some  building  ordinances 
require  that  blocks  shall  be  made  solid  for  several  courses 
underneath  the  point  that  bears  the  joist  load.  Such  blocks, 


CONCRETE  BUILDING  BLOCKS 


5 


however,  impair  the  air  space  in  the  wall,  and  the  precaution 
seems  to  be  an  unnecessary  one,  especially  if  a  metal  plate  is 
introduced  to  distribute  the  load  of  the 
joist. 

9.  Fastening  of  Roof  Plates. — For 

fastening  roof  plates  to  the  top  of  concrete 
walls,  Y-shaped  pieces  of  iron,  as  shown  in 
Fig.  2,  are  employed.  One  end  of  each 
device  is  embedded  in  mortar  joints  be¬ 
tween  two  blocks,  and  the  other  end,  which 
is  threaded,  is  passed  through  the  roof 
plate  and  secured  to  it  by  means  of  a  nut.  These  devices  are 
made  in  two  lengths  and,  as  shown,  are  placed  so  that  the 
strain  will  not  come  on  a  single  course  of  blocks. 


Fig.  1 


10.  Pi  lasters. — In  any  concrete-block  construction 
where  the  depth  of  a  building  exceeds  50  feet  and  where 
there  are  no  concrete-block  cross-partitions,  it  is  essential  to 
good  construction  that  pilasters,  or  buttresses,  be  placed  at 
intervals  of  25  to  40  feet.  The  pilasters  not  only  give  lateral 
strength  to  the  wall,  but  also  provide  stiffeners  in  case  of 
extreme  expansion  and  contraction  of  a  long  girder. 

An  example  of  such 
walls  is  shown  in 
Fig.  3,  where  the 
building  ab  f  e  has 
long  walls  a  b  a^id 
e  f  not  supported  by 
any  cross-partitions. 
The  pilasters  c,  d,  g, 
and  h  have  been 
added  to  strengthen 
the  walls  against 
stresses  caused  by 
expansion  and  con¬ 
traction  of  girders 

extending  from  the  wall  a  b  to  the  wall  e  f.  The  pilasters  in 
°  « 

this  instance  are  shown  on  the  inside  of  the  building. 


6 


CONCRETE  BUILDING  BLOCKS 


§37 


11.  Provision  for  Nailing. — The  problem  of  nailing 
interior  finish,  door  casings,  etc.  to  concrete-block  walls  has 
presented  some  difficulty  and  often  necessitated  the  embed¬ 
ding  in  the  blocks  of  wooden  strips  or  blocks  into  which 
nails  or  screws  might  be  driven.  A  more  happy  and  lasting 


Fig.  3 


solution  of  the  problem  is  the  patented  metal  nailing  plug 
shown  in  Fig.  4.  This  comparatively  inexpensive  device  is 
inserted  in  the  mortar  joints  as  the  blocks  are  laid. 

12.  Concrete-Block  Partitions. — The  better  practice 
where  fireproof  construction  is  desired  demands  partitions 
of  concrete  blocks.  The  blocks  lend  themselves  with  great 
readiness  to  this  use,  and  do  not  conduct  sound  so  readily  as 
the  ordinary  partition.  The  use  of  block  partitions  greatly 
strengthens  the  entire  structure,  affording  ample  bracing  of 

walls  and  giving  great  rigidity 
to  floors. 


BLOCKS  FOR  SPECIAL  USES 

13.  Blocks  for  Jambs. 

Fig.  4  Window  and  door  jambs  pre¬ 

sent  a  very  important  part  of  block  construction.  The 
exposed  portion  of  the  return  at  the  opening  must,  of  course, 
have  a  texture  similar  to  that  of  the  surface  of  the  wall. 
The  various  styles  of  jambs  for  boxed  construction,  etc. 
common  in  many  buildings  are  provided  for  in  most 


§  37 


CONCRETE  BUILDING  BLOCKS 


7 


block  machines.  It  is  important  that  these  jamb  blocks  be 
especially  well  made  and  cured,  because  they  are  more  liable 
to  severe  service  than 
most  parts  of  the 
building,  and  in  case 
of  an  interior  fire  are 
directly  exposed  to 
the  flames. 

14.  Blocks  for 
Corners. — The  cor¬ 
ner  blocks  are  very 
important  members  of  a  building.  As  noted  elsewhere,  their 
form  is  determined  by  the  machine  selected.  Some  designs 
use  the  stretcher  block  with  the  end  made  flush,  as  at  a , 
Fig.  5,  and  others  use  an  L  shape  with  the  return  half  the 
stretcher  length  as  at  a,  Fig.  6.  The  two-piece  systems  pro¬ 
vide  a  special  shape  for  corners.  In  any  system  of  concrete- 
block  construction,  the  corner  block  should  be  of  a  shape  that 
will  admit  of  great  structural  rigidity;  and,  besides,  in  manu¬ 
facturing  corners,  especial  care  should  be  taken  to  see  that 
each  one  is  as  strong  and  perfect  as  it  is  possible  to  make  a 
block.  It  is  wise  to  counsel  the  workmen  to  disregard  speed 
and  to  seek  absolute  perfection  in  the  manufacture  of  corner 
blocks.  The  number  used  in  a  building  is  comparatively 
small,  and  the  importance  of  each  is  relatively  great. 


15.  Blocks  for 
Chimney  Flues. 
Chimney  flues  are 
constructed  by  care¬ 
fully  closing  joints 
in  one-piece  blocks 
so  that  the  air  cavities 
will  form  a  perpen¬ 
dicular,  continuous, 
hollow  space  that 
may  serve  as  a  flue,  except  in  those  cases  where  the  hollow 
space  in  the  wall  does  not  afford  a  flue  of  sufficient  size. 


8 


CONCRETE  BUILDING  BLOCKS 


§37 


In  such  cases,  it  is  necessary  to  use  the  special  chimney 
block ,  which  is  a  recognized  part  of  the  system  of  blocks 
provided  in  the  adjustability  of  most  of  the  standard  makes 
of  machines,  and  which  results  in  the  creation  of  an  interior 
or  an  exterior  pilaster  according  to  the  fancy  of  the  building 
designer. 

16.  Blocks  for  Sills,  Lintels,  and  Ornamental 
Members. — The  making  of  sills,  lintels,  caps,  coping,  steps, 
belt  courses,  balustrades,  and  ornamental  work  in  general 
is  not  usually  provided  for  in  a  concrete-block  machine,  but 
the  equipment  necessary  to  produce  some  or  all  of  these 
members  is  a  necessary  adjunct  to  the  thoroughly  equipped 
plant.  In  the  earlier  days  of  the  industry,  the  more  plain 
of  these  special  parts  were  usually  produced  in  wooden  molds 
constructed  at  the  plant  as  occasion  demanded,  while  those 
requiring  greater  ornamentation  were  made  in  plaster  molds 
that  were  broken  to  release  the  undercut,  or  part  of  the 
bottom  mold  was  made  of  elastic  glue  to  allow  the  withdrawal 
of  the  part  of  the  block  that  was  provided  with  an  undercut 
ornamentation.  In  some  cases,  ornamental  work  was,  and 
still  is,  molded  in  sand.  This  process  is  highly  satisfactory 
in  the  hands  of  a  skilled  operator.  In  molding  in  sand,  there 
is  used  a  sectional  pattern,  around  which  the  sand  is  well 
tamped,  as  in  iron  molding.  The  pattern  is  then  removed  and 
the  concrete,  usually  of  a  fine  aggregate  and  made  wet  enough 
to  run,  is  poured  into  the  sand  mold  and  allowed  to  remain 
for  48  hours  or  longer,  according  to  the  size  of  the  castings. 

17.  The  demand  for  such  members  has  increased  so 
steadily  and  the  profit  in  their  manufacture  and  sale  has  been 
so  satisfactory  that  there  has  arisen  an  active  demand  for 
molds  in  which  the  work  can  be  produced  without  the  highly 
skilled  labor  required  in  using  plaster  and  glue  molds  and  in 
casting  in  sand.  To  meet  this  need,  several  companies  have 
entered  the  field  with  a  line  of  iron  molds  that  are  simple  in 
construction  and  operation,  and  in  which  the  same  mixture 
and  methods  common  in  block  making  produce  a  satisfactory 
grade  of  work.  This  line  of  molds  is  constantly  growing,  new 


§37 


CONCRETE  BUILDING  BLOCKS 


9 


designs  being  added  from  month  to  month,  and  the  pro¬ 
gressive  block  maker  will  not  fail  to  equip  his  plant  with 
the  molds  required  to  meet  the  demands  of  his  customers. 
Indeed,  a  very  good  business  can  be  done  in  making  orna¬ 
mental  pieces,  porch  columns,  balustrades,  lawn  vases,  etc., 
independent  of  general  block  construction.  Such  pieces 
molded  in  concrete  can  be  produced  much  cheaper  than 
similar  designs  in  stone,  and  if  well  made  they  will  prove  to 
be  just  about  as  durable. 

In  the  manufacture  of  sills  and  lintels,  whether  made  in  a 
mold  purchased  for  the  purpose  or  in  one  improvised  for  the 
particular  need,  it  is  well  to  insert  reinforcements  in  the  block 
near  the  bottom  in  case  the  length  exceeds  4  feet.  With 
proper  reinforcements,  lintels  can  be  made  to  span  any  desired 
opening  without  noticeable  deflection,  but  an  unreinforced 
lintel  with  a  span  of  7  or  8  feet  is  liable  to  fail,  owing  to  the 
load  brought  upon  its  center  from  the  walls  above. 


CAUSES  OF  FAILURES  IN  THE  BLOCK  INDUSTRY 

18.  Although  concrete  blocks  possess  the  greatest  possi¬ 
bilities  of  any  building  material,  it  is  a  fact  that  they -have 
in  many  instances  fallen  far  short  of  the  results  of  which  they 
are  capable.  There  is  absolutely  no  reason  for  the  production 
of  poor  blocks,  and  until  good  work  is  done  in  all  concrete- 
block  plants,  this  building  material  will  not  attain  the  prestige 
it  deserves. 

One  cause  of  failure  in  the  concrete-block  industry  is  that 
the  manufacture  has  been  regarded  as  too  easy.  It  has 
appeared  that  the  mere  mixing  of  sand  and  cement  and  the 
shaping  of  this  mixture  into  a  building  block  in  an  iron  mold  is 
a  process  requiring  little  skill  and  scant  knowledge,  while  the 
fact  that  the  product  can  be  sold  at  a  good  profit  and  still 
come  under  ruling  prices  of  brick  has  appealed  to  very  many 
men  who  in  no  wise  were  fitted  for  the  work.  As  a  result, 
many  plants  were  started.  These  plants,  however,  turned 
out  a  product  that  was  unsatisfactory  to  builders,  and  in  one 


10 


CONCRETE  BUILDING  BLOCKS 


§37 


or  two  seasons  caused  the  block  machine  to  be  offered  for  sale, 
second  hand,  or  consigned  to  the  scrap  heap,  while  concrete 
blocks  in  the  community  in  which  the  plant  was  located 
received  a  bad  name  that  it  might  take  many  years  to  outlive. 

Another  cause  of  failure  is  that  there  has  been  too  much 
talk  of  cheapness  in  connection  with  the  industry.  This 
talk  about  the  low  cost,  even  below  that  of  frame  construction, 
has  taken  such  a  firm  hold  on  the  mind  of  the  thoughtless 
manufacturer  that  he  rushes  into  contracts  without  ascertain¬ 
ing  what  the  blocks  really  cost.  Perhaps  he  knows  the  cost 
of  his  plain  wall  blocks,  but  is  unmindful  of  the  added  expense 
incident  to  special  blocks  of  various  shapes  required  in  every 
building.  Under  such  conditions,  a  profit  is  scarcely  to  be 
expected,  while  the  temptation  is  very  strong  to  reduce 
quality  in  order  to  avoid  loss. 


CONCRETE-BLOCK  COST  AND 
SPECIFICATIONS 


COST  OF  CONCRETE  BLOCKS 

19.  The  cost  of  concrete  blocks  is  an  important  and  prac¬ 
tical  consideration,  as  no  plant  is  started  except  with  the 
hope  of  profit.  It  was  inevitable  in  the  early  introduction 
of  concrete-block  machines  that  the  low  cost  of  the  blocks 
in  comparison  with  other  building  materials  should  be  pre¬ 
sented  as  one  of  the  chief  arguments  to  those  about  to  engage 
in  the  industry.  Also,  it  is  unfortunate  that  the  claims  made 
by  manufacturers  and  agents  resulted  in  a  widespread  belief 
that  concrete  blocks  were  a  cheap  building  material.  So 
eagerly  did  the  public  grasp  this  idea  that  the  block  maker, 
in  order  to  maintain  this  belief  resorted  to  making  blocks 
cheap  at  the  expense  of  quality.  The  results  in  many  cases 
have  been  deplorable  and  sometimes  disastrous.  But  a 
reaction  has  come,  and  the  public  is  now  demanding  quality, 
for  which  it  is  willing  to  pay  a  reasonable  price.  Persons-  that 


§37 


CONCRETE  BUILDING  BLOCKS 


11 


have  given  any  study  to  concrete  blocks  recognize  that  their 
worth  places  them  easily  in  the  lead  of  building  materials, 
and  it  is  the  intrinsic  merit  of  thoroughly  good  blocks,  rather 
than  the  low  cost  of  indifferently  made  blocks,  that  com¬ 
mends  them  to  the  conservative  builder. 

20.  A  careful  consideration  of  cost  will  give  the  block 
maker  data  by  which  to  calculate  the  actual  cost,  for  labor 
and  material,  of  each  kind,  size,  and  shape  of  block  that  he 
offers  for  sale.  Few  plants  have  this  data  so  carefully  tabu¬ 
lated  that  the  manufacturer  may  be  sure  he  is  not  losing  money 
at  some  point  in  the  business.  It  is  impossible  to  give  this 
information  in  such  a  form  that  it  will  apply  to  local  condi¬ 
tions.  It  must  be  computed  at  and  for  each  individual  plant. 

The  first  step  is  to  ascertain  the  cost  per  cubic  foot  of  each 
ingredient  used  and  from  these  figures  compute  the  cost  of 
each  mixture  used,  being  careful  to  reach  the  cost  of  a  cubic 
foot  of  the  mixture  at  that  degree  of  compression  which  it 
attains  in  the  completed  block.  Then  accurate  measure¬ 
ments  should  be  taken  to  determine  the  cubical  contents  of 
each  size  and  shape  of  block  made,  and  compute  the  cost  of 
material  it  contains.  The  additional  cost  of  face  matter 
should  not  be  overlooked.  To  the  cost  of  material  must  be 
added  the  labor  cost  of  each  kind  of  block,  figured  at  the 
average  rate  of  manufacture.  The  blocks  must  also  be 
assessed  with  cost  of  curing,  power,  superintendence,  machin¬ 
ery,  repairs,  and  rent  or  interest.  There  are  also  certain 
incidentals,  such  as  insurance,  advertising,  literature,  associa¬ 
tion  membership,  convention  attendance,  and  the  like,  that 
should  be  charged  against  the  estimated  or  actual  annual  out¬ 
put.  Depreciation  in  machinery  is  also  a  very  proper  charge 
that  is  too  often  disregarded.  If  all  these  things  are  consid¬ 
ered,  it  may  make  the  profits  appear  less,  but  it  will  certainly 
add  to  the  safety  of  the  business. 

If  blocks  are  sold  at  the  yard,  the  expense  will  cease  there, 
but  when  sold  delivered  at  the  building  site,  hauling  must  be 
included.  If  haulage  is  done  by  contract,  it  should  be  on  a 
basis  of  careful  handling,  with  blocks  so  loaded  that  they  will 


12 


CONCRETE  BUILDING  BLOCKS 


§37 


not  be  defaced.  The  most  convenient  method  of  separating 
faces  in  a  wagon  is  by  the  use  of  clean  straw.  If  the  block 
maker  has  teamsters  of  his  own,  he  will  secure  greater  care  in 
handling  blocks,  but  the  cost  of  transportation  may  be  slightly 
increased. 

In  very  many  places,  especially  when  introducing  the 
material,  the  block  maker  must  also  figure  on  laying  the 
blocks.  If  this  can  be  done  by  piece  work,  a  great  burden 
will  be  taken  from  his  mind,  but  if  it  must  be  done  by  day 
labor,  he  will  do  well  to  ascertain  from  others  using  the  same 
style  of  block  what  results  they  get  from  a  given  number  of 
masons  and  helpers,  and  then  see  that  the  men  he  employs 
come  up  to  the  average. 

21.  As  a  very  rough  figure,  which  varies  much  with  local 
conditions,  the  following  illustration  will  serve  to  show  the 
cost  of  concrete-block  construction:  Suppose  that  the  block 
exposes  2  square  feet  of  surface  in  the  wall,  is  8  inches  thick, 
and  has  an  air  space  of  the  total  volume.  The  material 
in  this  block  would  be  almost  1  cubic  foot,  and  would  cost 
form  6  to  18  cents.  The  cost  of  labor  varies  from  6  to  10^ 
cents  per  block.  To  lay  a  block  in  the  wall  costs  from  5  to 
10  cents,  including  mortar.  Haulage  will  cost  probably  5 
cents.  Therefore,  the  cost  per  block  8  inches  thick  set  in  the 
wall  is  as  follows: 

Maximum  Cost  Minimum  Cost 
Cents  Cents 


Material .  18  6 

Labor .  10£  6 

Placing .  10  5 

Haulage .  5  None 


434  17 

These  results  divided  by  2  give  the  cost  per  square  foot  of 
wall,  because  each  block  was  assumed  to  present  2  square 
feet  of  surface. 


§37 


CONCRETE  BUILDING  BLOCKS 


13 


SPECIFICATIONS 

22.  While  it  is  perhaps  impossible  to  submit  a  set  of 
specifications  that  may  meet  the  requirements  in  all  cases, 
the  following  is  an  attempt  to  give  certain  rules  governing  the 
manufacture  of  concrete  blocks,  not  with  any  claim  to  finality 
or  completeness,  but  rather  as  a  suggestion  that  may  serve 
as  a  basis  for  such  standard  specifications  as  may  secure  safety 
to  the  user  and  justice  to  the  maker  of  concrete  blocks,  both 
in  the  matter  of  town  and  city  requirements  and  in  that  other 
really  important  matter  of  insurance  rates: 

23.  Cement. — The  cement  used  shall  be  a  true  Portland  in 
the  sense  in  which  that  term  is  accepted  by  the  Association  of  American 
Portland-Cement  Manufacturers.  It  shall  be  delivered  at  the  place  of 
manufacture  in  cloth  or  paper  packages,  each  containing  1  cubic  foot 
of  cement,  and  each  having  a  net  weight  of  94  pounds.  It  shall  be 
kept,  until  required  for  use,  in  good,  dry  storage.  It  shall  fully  meet 
the  requirements  of  the  tests  specified  by  the  American  Society  for 
Testing  Materials.  In  use,  it  shall  be  measured  by  weight,  except  that 
when  a  sack  is  taken  as  the  unit  it  may  be  considered  as  94  pounds. 

24.  Sand. — The  sand  shall  be  siliceous  and  clean.  It  shall 
include  no  particles  retained  on  a  screen  of  -|--inch  mesh.  In  the 
selection  of  sand,  preference  shall  be  given,  first,  to  a  sand  compri¬ 
sing  graduated  sizes  of  grains,  and  second,  to  a  coarse  sand.  The 
sand  shall  be  free  from  loam,  clay,  and  vegetable  or  animal  matter. 
If  not  free  from  such  foreign  matter  in  its  natural  state,  it  shall  be 
washed  until  the  washing  water  is  no  longer  discolored. 

25.  Gravel. — The  gravel  shall  include  the  particles  that  will 
pass  through  a  f-inch  ring  and  be  retained  on  a  screen  of  j-inch  mesh. 
Preference  shall  be  given,  first,  to  gravel  graduated  in  size  from  fine 
to  coarse;  and,  second,  to  gravel  that  is  irregular  in  shape  and  of  a 
rough  exterior.  The  gravel  shall  accord  in  respect  to  cleanliness  and 
freedom  from  foreign  matter  to  the  foregoing  specification  for  sand. 

26.  Stone  . — Crushed  granite,  trap  rock,  or  limestone  may  be 
used,  as  hereinafter  specified,  to  replace  gravel,  sand,  or  both  gravel 
and  sand,  except  that  limestone  shall  not  be  used  in  blocks  guaranteed 
against  fire.  What  is  commonly  known  as  crusher  run  shall  not  be 
used  without  rescreening.  As  a  substitute  for  gravel,  the  pieces 
that  are  retained  on  a  screen  of  j-inch  mesh  and  pass  a  f -inch  ring  may 
be  used.  As  a  substitute  for  sand,  the  particles  that  pass  a  screen 


CONCRETE  BUILDING  BLOCKS 


14 


§37 


of  -^--inch  mesh  may  be  used,  and  such  particles  shall  be  known  as 
screenings. 

27.  Proportions. — In  a  block  the  largest  aggregate  of  which 
passes  a  screen  of  ^-inch  mesh,  the  minimum  proportion  shall  be  1  part 
of  cement  to  4  parts  of  sand  or  stone  screenings,  and  such  propor¬ 
tions  shall  be  by  weight.  In  a  block  the  largest  aggregate  of  which 
is  retained  on  a  screen  of  -^-inch  mesh,  the  minimum  proportion  of 
cement  shall  be  1  part  of  cement  to  7  parts  of  mixed  aggregate,  and 
said  7  parts  of  aggregate  may  vary  in  proportioning  from  2  parts  of 
sand  or  screenings  and  5  parts  of  gravel  or  stone  to  3  parts  of  sand  or 
screenings  and  4  parts  of  gravel  or  stone,  and  said  proportions  shall  be 
by  weight.  The  proportioning  shall  in  every  case  be  based  on  deter¬ 
mination  of  voids,  either  by  specific  gravity,  by  relative  volume,  or  by 
water  test.  If  the  last  method  is  used,  it  shall  be  subject  to  check 
by  the  preceding.  The  proportion  of  sand  shall  in  every  case  exceed 
the  determined  voids  in  the  gravel  or  stone  by  at  least  5  per  cent., 
and  the  proportion  of  cement  shall  in  every  case  exceed  the  deter¬ 
mined  voids  in  the  combined  aggregate  by  at  least  10  per  cent. 

28.  Coloring  Matter. — All  coloring  matter  other  than  colored 
stone  or  screenings  shall  be  a  pure  mineral  color  and  shall  be  mixed 
dry  with  the  cement  before  being  added  to  the  aggregate. 

29.  Mixing  . — If  mixing  is  done  by  hand,  it  shall  be  upon  a 
water-tight  platform  on  which  the  gravel  or  stone  shall  first  be  spread, 
the  sand  or  screenings  spread  thereon,  and  the  cement  spread  on  top 
of  the  sand  or  screenings.  Before  water  is  added,  the  mass  shall  be 
turned  twice,  or  until  of  a  uniform  color.  Water  shall  then  be  added 
by  spray  or  by  gently  pouring  into  a  crater  formed  of  the  dry  material. 
The  mass  shall  then  be  turned  three  times,  or  until  of  uniform  con¬ 
sistency. 

If  mixing  is  done  mechanically,  the  dry  aggregate  and  cement  shall 
first  be  placed  in  the  mixer  and  well  mixed  before  water  is  added,  and 
when  water  is  added,  the  mixing  shall  continue  as  long  as  necessary 
to  secure  homogenity  in  the  mass. 

All  material  to  which  cement  has  been  added  shall  be  used  within 
30  minutes  from  the  time  water  is  added. 

30.  Consistency. — For  the  purposes  of  these  specifications 
there  shall  be  three  grades  of  consistency  of  concrete,  as  follows : 

1 .  Dry  concrete,  by  which  is  meant  a  mixture  that  on  being  pressed 
in  the  hand  retains  its  shape  but  does  not  discolor  the  hand,  shall  never 
be  used  for  the  body  of  the  block. 

2.  Medium  concrete,  by  which  is  meant  a  mixture  from  which, 
when  thoroughly  tamped  or  pressed,  free  water  will  flush  to  the  surface, 
shall  be  used  for  the  body  of  all  tamped  or  pressed  blocks. 


§37 


CONCRETE  BUILDING  BLOCKS 


15 


3.  Wet  concrete ,  by  which  is  meant  a  mixture  that  can  be  readily 
poured  from  a  bucket  into  a  mold,  shall  be  used  in  all  processes  where 
the  block  or  other  member  is  subjected  to  neither  tamping  nor  pressure, 
but*  acquires  the  form  of  the  mold  by  its  own  settlement  and  attains 
rigidity  by  remaining  therein. 

31.  Condensation. — Condensation  may  be  effected  by  tamp¬ 
ing,  pressing,  or  pouring. 

1.  The  material  may  be  condensed  in  the  mold  by  hand  or  power 
tamping.  In  either  case,  the  material  shall  be  deposited  in  layers  of 
such  depth  that  the  full  force  of  the  tamping  blow  is  exerted  on  every 
portion  of  the  block,  and  the  tamping  shall  be  so  regulated  that  the 
density  shall  be  uniform  in  every  part  of  the  block  and  relatively  equal 
in  each  block. 

2.  The  material  may  be  condensed  in  the  mold  by  mechanical 
or  by  hydraulic  pressure.  In  either  case,  the  mold  shall  be  filled  and 
the  entire  block  compressed  at  one  time  by  a  minimum  pressure  of 
350  pounds  to  the  square  inch  of  the  face  surface  of  the  block. 

3.  The  material  may  be  condensed  by  its  own  settlement  in  a 
mold  of  metal  or  of  sand.  In  either  case,  the  material  shall  be  mixed 
so  wet  that  it  is  easily  poured  into  the  mold  and  readily  acquires  the 
form  thereof,  and  it  shall  remain  therein  until  it  gains  sufficient 
rigidity  to  maintain  its  shape  without  support. 

32.  Facing. — If  a  block  is  faced  with  a  mixture  other  than 
that  used  for  the  body  of  the  block,  the  aggregate  for  the  face  matter 
shall  be  of  fine  sand,  fine  stone  screenings,  marble  dust,  or  other  suit¬ 
able  material  mixed  with  the  cement  in  proportions  that  may  vary 
from  1  part  of  cement  and  1  part  of  aggregate  to  1  part  of  cement  and 
3  parts  of  aggregate. 

Note. — Either  1-2^  or  1-3  is  recommended  as  possessing  less  liability  to  hair  cracks 
than  a  richer  mixture. 

In  no  case  shall  the  face  be  troweled  either  before  or  after  molding. 

Coloring  matter  may  be  added  as  specified  in  Art.  28. 

Face  matter  shall  be  mixed  in  consistency  of  dry  concrete,  as  speci¬ 
fied  in  Art.  30.  After  moistening,  the  face  matter  shall  have  all 
lumps  broken  up  by  rescreening  immediately  before  using. 

The  face  matter  shall  be  deposited  from  a  sieve  or  by  loosely 
shaking  it  from  a  shovel,  so  that  it  will  maintain  its  loose  form  until 
deposited  in  the  mold. 

The  method  of  condensing  the  material  in  the  mold  shall  bear  such 
relation  to  the  face  matter  that  the  face  will  become  firmly  joined  to 
the  body  of  the  block,  so  that  it  can  be  removed  only  by  the  destruc¬ 
tion  of  the  block. 


10  CONCRETE  BUILDING  BLOCKS  §  37 

33.  Curing.  — The  minimum  age  of  blocks  at  time  of  placing 
in  wall  shall  be  3  weeks.  Curing  may  be  by  water  or  by  steam. 

1.  Water  Curing. — Sprinkling  shall  begin  as  early  as  possible 
without  defacement — under  average  conditions  12  hours  after  mold¬ 
ing — and  shall  continue  at  such  intervals  as  necessary  to  maintain  a 
thorough  and  uniform  degree  of  moisture  for  from  7  to  10  days,  during 
which  period  the  block  shall  not  be  exposed  to  sun,  wind,  or  violent 
change  of  temperature. 

2  Steam  Curing. — The  blocks  shall  be  kept  in  moist  air  for  24 
hours  after  molding,  when  they  shall  be  placed  in  a  tightly  closed 
room  into  which  exhaust  steam  or  live  steam  of  low  pressure  is  turned, 
remaining  in  said  steam  room  for  36  hours,  after  which  they  shall 
be  sprinkled  and  protected  from  sun  and  wind  for  a  further  period  of 
48  hours. 

34.  Taying. — Blocks  shall  be  thoroughly  moistened  before 
laying  in  the  wall,  and  shall  be  laid  in  a  mortar  consisting  of  1  part  of 
cement  to  3  parts  of  sand,  or  1  part  of  cement,  1  part  of  thoroughly 
slaked  and  pulverized  lime,  and  3  parts  of  sand.  The  mortar  joints 
shall  be  of  uniform  thickness,  not  exceeding  f-inch 

35.  Ail*  Space. — The  air  space  in  the  wall  shall  be  governed 
by  the  type  of  block  and  the  thickness  of  wall,  but  the  minimum  thick¬ 
ness  of  face  section,  back,  and  transverse  webs  shall  in  every  case 
be  2  inches. 

36.  Width  of  Walls. — The  width  of  walls,  in  inches,  for  the 
several  heights  of  buildings,  and  for  the  several  stories  thereof,  shall 
be  as  follows: 


First 

Second 

Third 

Fourth 

Story 

Story 

Story 

Story 

One-story  buildings . 

.  8 

Two-story  buildings . 

.  10 

10 

Three-story  buildings . 

.  12 

12 

10 

Four-story  buildings . 

.  15 

15 

12 

10 

37.  Testing  . — Blocks  for  testing  shall  be  selected  at  random 
from  those  commercially  manufactured  or  delivered  at  building  site. 
The  minimum  compressive  strength  of  any  block  shall  be  1,600  pounds 
per  square  inch  of  solid  material  subjected  to  pressure  in  the  testing 
machine,  and  the  average  compressive  strength  of  any  series  of  blocks 
tested  shall  not  be  less  than  1,800  pounds  to  the  square  inch  of  such 
solid  material. 

Blocks  shall  also  be  subjected  to  such  tensile,  fire,  freezing,  and 
absorption  tests  as  may  be  required  by  the  supervising  engineer. 

38.  Identification. — Each  block  shall  be  marked  with  the 
initials  of  the  manufacturer  thereof  and  the  date  of  molding. 


§37 


CONCRETE  BUILDING  BLOCKS 


17 


39.  Certificate. —  Each  manufacturer  of  blocks  shall  post 
in  a  conspicuous  position  at  his  place  of  business  a  certified  test, of 
blocks  actually  manufactured  by  him  in  regular  course  of  business, 
which  certificate  shall  show:  (1)  The  size,  number,  age  and  composi¬ 
tion  of  blocks  tested;  (2)  the  compressive  strength  of  each  block 
tested,  and  the  average  result  of  the. series  tested  for  compression;  and 
(3)  the  results,  in  like  manner,  of  such  other  tests  as  may  be  required 
by  the  building  department  of  the  town  or  city  in  which  the  blocks 
are  offered  for  sale. 


I  . 


4 


*■» 


HEAVY  FOUNDATIONS 


SPREAD  FOOTINGS 


SINGLE  FOOTINGS 


INTRODUCTION 

1.  The  term  spread  footings  is  applied  to  the  class  of 
foundations  illustrated  in  Figs.  1  and  2.  Foundations  of  this 


Fig.  1 


kind  are  best  adapted  for  the  substructure  of  high  buildings 
that  are  to  be  erected  on  soil  of  a  clayey  nature,  and  are 

i 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS'  HALL.  LONDON 

§  38 


211—25 


2 


HEAVY  FOUNDATIONS 


§38 


especially  necessary  where  the  foundation  stratum  is  of  soft 
clay  underlaid  with  quicksand  and  the  bed  rock  is  so  far 
below  the  foundation  bottom  as  to  preclude  the  possibility 
of  driving  piles  to  a  bearing  on  it.  Spread  footings  may  also 
be  used  to  advantage  on  any  soil  where  it  is  necessary  to 
distribute  the  load  over  a  considerable  area.  With  such  a  soil, 
there  are  many  details  that  require  careful  attention  and 
study  and  involve  the  incorporation  of  several  features  new 
to  the  usual  stepped  masonry  foundations. 

Tall  buildings  of  the  skeleton-construction  type  concentrate 
great  loads  on  the  basement  columns;  these,  in  turn,  must 


be  supported  by  footings  of  considerable  area.  As  the 
exterior  columns  in  this  type  of  building  support  the  out¬ 
side,  or  curtain,  walls,  they  are  more  heavily  loaded  than  the 
interior  columns;  and  since  some  settlement  is  sure  to  occur, 
it  is  desirable  that  this  settlement  be  uniform.  The  simplest 
way  to  attain  uniformity  in  settlement  is  to  provide  a  sepa¬ 
rate  footing  for  each  column  or  set  of  columns  that  acts 
in  unison,  the  entire  building  being  in  this  way  supported 
on  isolated  footings  that  are  accurately  proportioned  for 
the  loads  they  must  sustain.  If,  as  shown  in  Fig.  3  (a), 


(a) 


6 


5-7- - J  ^ - 13-5 


4 


HEAVY  FOUNDATIONS 


§38 


these  footings  were  of  the  usual  masonry  type  and  had  the 
proper  proportions  and  batter  for  this  material,  they  would 
be  of  great  depth  and  of  such  dimensions  as  to  lessen  consider¬ 
ably  the  floor  space  in  the  basement  of  the  building.  This 
amount  of  masonry  would  add  greatly  to  the  unit  weight 
on  the  soil  and  would  form  a  considerable  percentage  of  the 
entire  load. 

2.  A  recapitulation  of  the  requirements  that  lead  to  the 
adoption  of  spread  footings  may  be  stated  as  follows: 

1.  That  sufficient  bearing  may  be  obtained  for  the  great 
loads  requiring  support  in  the  modern  tall  building  resting 
on  a  plastic  or  an  unstable  soil. 

2.  That  the  foundation  and  footing  may  be  so  shallow  as 
not  to  penetrate  the  stratum  of  clay  and  impair  its  bearing 
value  when  underlaid  with  quicksand. 

3.  That  no  foundation  piers  of  great  bulk  occupy  space 
in  the  basement  that  may  be  used  for  engine  rooms  or  even 
bring  in  a  good  rental  as  cafes  or  shops. 

4.  That  the  weight  of  the  foundation  shall  be  so  small  a 
percentage  of  the  entire  load  on  the  column  it  sustains 
that  a  considerable  portion  of  the  footing  area  will  not  be 
taken  up  in  carrying  the  weight  of  the  foundation. 

5.  That  the  cost  of  the  foundation  shall  not  greatly 
exceed  the  cost  of  the  usual  stepped  footings  or  foundation 
piers  of  masonry. 

The  second  and  third  requirements  are  of  considerable 
importance,  and  by  referring  to  Fig.  3,  the  advantages  that 
the  spread  footing  possesses  over  the  ordinary  masonry 
footing  will  be  evident,  especially  with  regard  to  space  saved 
in  the  basement  and  the  depth  required  for  the  respective 
constructions.  In  (a)  is  shown  the  ordinary  masonry  pier 
with  a  concrete  footing,  while  in  ( b )  is  illustrated  a  spread 
footing  designed  for  the  same  load  and  conditions  of  soil. 
By  comparing  these  views,  it  will  be  observed  that  a  depth 
of  nearly  8  feet  is  saved  by  the  use  of  the  spread  footing. 

3.  Spread  footings  may  be  classified  as  steel-beam  gril¬ 
lage  and  reinforced-concrete  foundations.  These  two  methods 


§  3S 


HEAVY  FOUNDATIONS 


of  construction  are  shown  in  Figs.  1  and  2,  respectively. 
They  both  produce  the  same  results,  namely,  a  shallow 
footing  that  has  a  large  bearing  area  on  the  soil  and  that 
possesses  sufficient  transverse  strength  to  transmit  a  great 
pressure  from  the  comparatively  small  area  of  the  column 
base  to  the  large  area  of  the  foundation  footing.  In  the 
steel-beam  grillage  foundation,  the  transverse  strength  is 
supplied  by  the  resistance  offered  by  the  steel  beams  to 
bending,  while  in  the  reinforced-concrete  footing  the  necessary 
transverse  resistance  is  provided  by  embedding  a  network  of 
steel  tension  bars  in  the  lower  portion  of  the  concrete, 
as  shown  at  a,  Fig.  2.  Reinforced-concrete  spread  footings 
are  discussed  at  length  in  another  Section. 


STEEL-BEAM  GRILLAGE 

4.  The  beams  originally  employed  in  the  construction  of 
grillage  footings  were  steel  rails  crossed  in  alternate  layers. 
Undoubtedly,  they  were  used  on  account  of  being  readily 
obtainable.  The  top  layer  of  steel  beams,  that  is,  those 
directly  under  the  cast-iron  base,  usually  have  as  much 
projection  as  any  of  the  under  layers,  and  being  fewer  in 
number,  are  required  to  offer  greater  resistance  to  bending; 
therefore,  in  most  cases,  steel  I  beams  with  a  section  modulus 
greater  than  steel  rails  were  used  in  this  position.  Now 
that  rolled  structural  shapes  are  obtained  with  facility, 
it  is  more  economical  to  use  I  beams  throughout  the  footing, 
where  its  height  is  not  closely  limited,  as  their  weight  is  less 
for  a  given  section  modulus  than  steel  rails.  Another  advan¬ 
tage  exists  in  the  fact  that  I  beams  may  be  readily  secured 
together  with  bolts  and  separators. 

If  the  soil  is  soft  and  plastic  and  the  load  heavy,  a  large 
area  of  footing  will  be  required.  To  obtain  this  area,  three  or 
more  tiers  of  beams  are  required,  and  each  tier  must  be  of 
larger  area  than  the  one  that  rests  on  it.  If  the  load  is 
light  and  the  soil  is  of  a  more  stable  character,  two  tiers 
of  beams  will  usually  be  sufficient.  Grillage  foundations 
are  either  square  or  rectangular,  depending  on  their  location 


6 


HEAVY  FOUNDATIONS 


§38 


in  the  footing  area.  For  the  support  of  a  single  column, 
square  foundations  are  preferable  and  more  economical. 
Rectangular  footings  are  used  where  the  space  available  is 
narrow  and  the  necessary  area  must  be  provided  by  lengthen¬ 
ing  the  footing. 

5.  The  usual  design  for  a  heavy  grillage  footing  is  shown 
in  Fig.  4.  It  is  necessary  to  provide  first  a  bed  of  concrete  a 
from  12  to  18  inches  in  thickness.  This  concrete  should  be 
tamped  in  two  or  three  successive  layers  and  should  be  com¬ 
posed  of  1  part  of  Portland  cement,  2  parts  of  sand,  and  5  parts 
of  broken  stone.  On  this  concrete  bed,  after  it  has  obtained 
its  initial  set,  the  first  layer  of  I  beams  is  placed,  the  spaces 


between  the  beams  being  solidly  tamped  with  concrete.  The 
beams  in  each  tier  are  firmly  secured  to  each  other  by  means  of 
separators  and  bolts.  The  separators  may  be  of  either  cast 
iron  or  pressed  steel;  pipe  separators  should  not  be  used. 
They  should  be  placed  not  more  than  6  inches  from  each  end 
of  the  beam,  and  one  should  be  placed  under  each  of  the 
outside  beams  in  the  tier  above.  Other  separators  should 
be  introduced  throughout  the  length  of  the  tier,  so  that  the 
distance  between  separators  will  in  no  case  exceed  5  feet. 
On  the  first  tier  of  beams,  the  second  layer  of  steel  beams 
is  crossed;  and  after  these  have  been  filled  in  with  concrete, 
the  third  layer  is  placed  in  position  and  embedded  in  con- 


§38 


HEAVY  FOUNDATIONS 


7 


Crete.  The  concrete  in  all  cases  is  placed  on  the  tops,  sides, 
and  ends  of  the  steel  beams  to  a  depth  of  from  4  to  6  inches, 
so  that  the  entire  steelwork  is  completely  embedded.  Before 
the  steel  beams  are  placed  in  position,  they  should  be  thor¬ 
oughly  painted  with  several  coats  of  some  good  preservative 
paint,  thus  protecting  the  steel  from  corrosion  until  the 
initial  set  of  the  concrete  takes  place.  When  this  precaution 
is  adopted,  the  steel  will  last  indefinitely,  provided  the 
concrete  contains  sufficient  cement.  In  placing  the  steel 
beams,  they  should  never  be  spaced  closer  than  3  inches 
in  the  clear  between  the  flanges,  so  that  the  concrete  may  be 
thoroughly  rammed  between  them. 


DESIGN  OF  SINGLE  FOOTINGS 

6.  In  designing  steel-beam  grillage  foundations  intended 
to  support  columns,  it  is  first  necessary  to  ascertain  the 
column  load  that  is  to  be  transmitted  to  the  footing.  It  is 
also  necessary  to  determine  the  area  required  for  the  footing 
in  order  that  the  allowable  unit  pressure  on  the  soil  may  not 
be  exceeded.  When  the  area  of  the  footing,  and  consequently 
its  dimensions,  has  been  determined,  the  lengths  of  the  steel 
beams  will  be  known.  However,  the  number  of  beams 
required,  as  well  as  their  size  and  their  weight,  must  be 
ascertained  by  calculation. 

The  steel  beams  that  provide  the  necessary  transverse 
strength  for  the  footings  are  subject  to  failure  by  the  crush¬ 
ing  or  buckling  of  the  web  or  by  bending.  Since  the  webs 
of  the  beams  are  secured  together  at  close  intervals  by 
separators  and  bolts,  and  since  concrete  is  thoroughly  tamped 
between  the  beams,  there  is  little  liability  of  the  webs  bulging 
or  crippling,  so  that  the  beams  may  be  considered  safe 
from  failure  if  the  unit  stress  on  the  web  due  to  direct 
compression  does  not  exceed  10,000  pounds.  Some  engineers 
consider  the  web  of  the  beam  as  a  column  and  thus  determine 
the  allowable  unit  compressive  stress.  When  column  for¬ 
mulas  are  applied  in  this  manner  to  determine  the  resistance 
of  the  web  to  bulging,  the  height  of  the  web  is  considered  as 


HEAVY  FOUNDATIONS 


8 


§38 


the  length  of  the  column  and  should  be  taken  as  the  distance 
between  the  fillets. 

The  proper  method  of  determining  the  bending  moment 
to  which  the  steel  beams  in  the  grillage  foundation  are 
subjected  has  been  a  matter  of  some  dispute  among 
engineers.  Some  engineers  consider  the  projecting  portion 
of  the  beam — that  is,  the  length  beyond  the  edge  of  the  cap 
or  the  successive  layer  above — as  a  cantilever,  while  others 
recommend  as  better  practice  that  the  entire  length  of  the 

beam  be  considered  and 
•Loac/  o/r  Co/umn=w  the  bending  moments  cal¬ 
culated  accordingly.  It  is 
doubtful  whether  either 
method  gives  the  true  value 
of  the  transverse  strength 
of  the  successive  tiers  of 
the  footing,  for  the  beams 
are  necessarily  reinforced 
by  the  concrete.  By  disre¬ 
garding  the  concrete,  how¬ 
ever,  the  problem  becomes 
greatly  simplified  and  any 
error  is  on  the  side  of 
safety.  The  formulas  for 
determining  the  bending 
moment  on  the  steel 
beams  in  a  grillage  foun¬ 
dation  may  be  derived  as 
pages. 


■*— V- -C  •  3HEE: 

(v  H'T 


x 


-I- 

V 


1.1 1  11  l 


ill  I  1 1  1 


LL.I1  J  1’3 


!1  II  III 


D 


s 


-  1  - 


V 


y-n-TTTr 


LiiJLLE 


xn 


XT 


EX 


h  d 

b 

I 

I 


i  i  i. 


XT 


I _ 


Fig.  5 


explained  in  the  following 


7.  In  Fig.  5  is  shown  the  plan  and  elevation  of  a  grillage 
footing.  The  area  has  been  determined  for  the  stability  of 
the  soil  and  the  magnitude  of  the  superimposed  load,  and  the 
dimensions  of  the  sides  thus  obtained.  The  superimposed 
load  transmitted  to  the  footing  through  the  column  may  be 
designated  as  W.  The  dimensions  of  the  cast-iron  base 
plate  are  practically  fixed  by  the  design  of  the  column;  at 
any  rate,  they  may  be  originally  assumed,  and  reduced  or 


HEAVY  FOUNDATIONS 


9 


§38 


increased  as  conditions  warrant.  It  is  therefore  considered 
that  the  distances  y  and  x  in  the  plan  are  found,  so  that 
the  length  for  the  top  tier  of  beams  is  equal  to  x  +  y  +  y 
=  x  +  2y.  The  load  on  these  beams,  since  they  transmit 
the  entire  weight  on  the  column,  is  equal  to  W,  and  the  load 
on  each  unit  of  length  of  the  tier  is,  in  consequence,  equal  to 


W 

The  steel  beams  in  the  first  tier,  being  considered 

x  +  2  y 

as  cantilevers  with  a  projection  equal  to  y  and  having  a 
center  of  moments  about  the  line  a  b,  sustain  the  uniformly 
distributed  load  acting  upwards  from  beneath,  equal  to  the 
load  per  unit  of  length  of  the  tier  multiplied  by  the  distance  y, 

Wy 


or,  as  it  may  be  stated, 


The  center  of  gravity  of 


x  +  2  y 

this  uniformly  distributed  load  is  along  the  line  c  d,  the  dis- 


y 

tance  .of  c  d  from  a  b  being  therefore,  the  bending  moment 
•  2 

of  all  the  beams  in  the  top  tier  is  equal  to  the  moment  of 
the  uniformly  distributed  load  on  the  projecting  portion  of 
the  tier  between  the  edge  of  the  cast-iron  base  and  the  ends 
of  the  beams,  or,  algebraically  expressed, 

Wf 


M  = 


2  (x  +  2  y) 


It  is  customary  to  take  all  the  lengths  in  inches  and  the 
weight  in  pounds;  then,  the  bending  moment  M  will  be  in 
inch-pounds. 

This  formula,  based  on  the  assumption  that  the  steel 
beams  are  cantilevers,  may  be  stated  as  in  the  following  rule: 


Rule. — The  bending  moment  on  the  beams  in  any  tier  is 
equal  to  the  quotient  obtained  by  dividing  the  product  of  the  load 
on  the  footing  and  the  square  of  the  distance  that  the  beams 
project  beyond  the  base  or  the  tier  of  beams  above ,  by  twice  the 
sum  obtained  by  adding  the  width  of  the  tier  or  base  above  and 
twice  the  projection. 


8.  The  resisting  moment  in  any  steel  beam  must  equal 
the  bending  moment;  hence,  M  =  and  Mt  =  S  s,  where  5 


10 


HEAVY  FOUNDATIONS 


§38 


equals  the  section  modulus  of  the  beam  section,  and  5  the 
unit  fiber  stress.  When  the  bending  moment  has  been 
determined  and  the  number  of  beams  in  the  tier  decided 
on,  the  required  section  modulus  for  each  beam  may  be 
obtained  by  the  formula 


s  n 


in  which  Mt  =  resisting  moment ; 

s  =  allowable  unit  fiber  stress ; 
n  =  number  of  steel  beams  in  tier. 


This  formula  may  be  expressed  as  follows: 


Rule. —  The  section  modulus  required  for  each  steel  beam  in 
a  grillage  footing  is  determined  by  dividing  the  resisting  moment 
necessary  for  the  entire  tier  by  the  product  of  the  safe  unit  fiber 
stress  and  the  number  of  beams. 

On  obtaining  the  necessary  section  modulus  for  each  of 
the  steel  beams  in  this  manner,  the  most  economical  beam 


§38 


HEAVY  FOUNDATIONS 


11 


section  may  be  determined  from  tables  giving  properties 
of  sections. 

Instead  of  assuming  the  number  of  beams  in  the  tier  and 
using  formula  1  to  find  the  required  section  modulus,  the 
size  of  the  beam  can  be  decided  on  and  the  number  required 
obtained  by  transposing  the  formula  thus, 


n  = 


M, 

s  S 


If  the  beams  determined  in  this  manner  are  too  great  in 
number  to  be  placed  under  the  cast-iron  cap  and  allow  at  least 
3  inches  between  the  flanges,  either  the  cap  must  be  increased 
in  width  or  deeper  and  heavier  beams  must  be  adopted. 
After  the  first  tier  of  beams  has  been  designed  and  the  size  of 
the  beams  determined  by  formula  1,  the  size  of  the  beams  for 
the  second  tier,  and  the  other  tiers  beneath,  may  be  computed. 

Example. — In  Fig.  6,  it  is  assumed  that  the  dimensions  of  the  foot¬ 
ings  are  as  shown  and  that  the  number  of  beams  in  each  tier  and  the 
dimensions  of  the  cast-iron  base  have  been  designed  as  shown  on  the 
plan.  What  should  be  the  size  of  the  steel  beams  in  each  tier  in  order 
to  provide  ample  support  for  the  load  of  400,000  pounds,  using  a 
safe  unit  fiber  stress  of  15,000  pounds? 

Solution. — The  bending  moment  on  the  upper  tier  of  beams  a  is, 

Wy2 

by  the  formula  of  Art.  7,  equal  to  M,  or - .  According  to 

y  H  2(x  +  2  y) 

the  conditions  of  the  problem  and  the  dimensions  given  in  the  figure, 

W  =  400,000  lb.,  y  =  5 6  in.,  and  x  =  30  in.  Then,  by  substitution, 

400,000X56X56  .  „  „  r  _  4 

M  = - =  4,416,901  in. -lb.  From  formula  1,  Art.  8,  the 

2(30  +  2X56) 

„  M, 

required  section  modulus  is  equal  to  S  —  — .  Since  M.=M,  the 

5  n 

value  of  Mj  in  the  problem  equals  the  result  just  obtained,  or  4,416,901 
in. -lb.;  s  taken  at  15,000  lb.  gives  a  factor  of  safety  of  at  least  4, 
which  is  ample,  and  n ,  the  number  of  beams  taken  from  the  figure, 
equals  6,  so  that  by  substituting  these  values  in  the  formula, 
4,416,901 

S  = — - - - =  49.08,  wdiich  is  the  section  modulus  required  for  each 

15,000X6  M 

beam  of  the  first  tier.  From  tables  giving  the  properties  of  sections, 

the  most  economical  I  beam  will  be  found  to  be  one  having  a  depth  of 

15  in.  and  a  weight  of  42  lb.  per  ft.  By  substituting  in  the  formula 


12 


HEAVY  FOUNDATIONS 


§38 


of  Art.  7 ,  the  bending  moment  on  the  beams  b  in  the  second  tier  is 
400,000X36X36 

equal  to  M  — - - - - —  =  2,107,317  in. -lb.  Then,  since  M ,  has 

2(51  +  2  +  36)  1 

been  determined  and  the  safe  unit  fiber  stress  is  15,000  lb.,  and  there  are 


fourteen  beams,  the  value  of  5,  from  formula  1,  Art.  8,  is  equal  to 
2  107  317 

— - - - - =10.035.  From  the  tables,  it  will  be  observed  that 

15,000X14 

beams  having  a  depth  of  7  in.  and  weighing  15  lb.  per  ft.  may  be  used 
in  the  bottom  tier.  Ans. 


9.  The  other  method  of  determining  the  transverse 
resistance  of  the  steel  beams  in  the  grillage  foundation  is 
more  reasonable  than  the  one  just  explained  and  is  therefore 
preferable.  In  this  method,  the  entire  length  of  the  beam  is 
considered  in  calculating  the  bending  moment,  and  the  loads 
on  the  beams  are  taken  as  they  actually  exist. 

For  instance,  in  Fig.  7  is  shown  a  steel-beam  grillage,  in 
elevation,  composed  of  three  tiers  of  beams.  In  analyzing 

the  bending  moment  on 
the  lower  tier  a,  it  will 
jfr  be  seen  that  the  total 

load  from  the  column 
acting  on  the  top  of  the 
beams  in  this  lower  tier 
is  distributed  over  only 
a  portion  of  the  length 
of  each  of  these  beams 
equal  to  c  b,  while  the 
reactions  acting  upwards  from  the  bottom  of  the  tier,  in  oppo¬ 
sition  to  the  weight  from  the  column,  are  distributed  over  the 
entire  length  equal  to  e  /,  the  entire  reaction  being,  of  course, 
equal  to  the  load  W.  The  condition  of  loading  that  then 


HEAVY  FOUNDATIONS 


13 


$  38 


exists  on  the  beams  is  diagrammatically  shown  in  Fig.  8, 
in  which  the  total  load  on  the  top  of  the  beams  is  equal 
in  amount  to  the  total  force  acting  upwards  from  the  bottom. 
The  greatest  bending  moment  under  such  a  condition  of  load¬ 
ing  does  not  actually  occur  at  the  edge  of  the  first  tier  of 
beams  g,  as  explained  in  Art.  7,  but  exists  at  the  center  c  of 
each  of  the  beams,  Fig.  8.  Then,  considering  the  point  c 
as  the  center  of  moments,  the  bending  moment  at  that 
point  will  be  equal  to  the  difference  between  the  moment 
of  the  force  acting  upwards  and  that  of  the  load  on  the 
beam  acting  downwards,  and  is  determined  according  to  the 
principle  of  moments. 


The  lever  arm  of  the  upward  force,  or  the  reaction,  is 

l  x 

equal  to  -  and  that  of  the  downward  force  is  equal  to  -,  or 

4  4 

the  distances  from  the  center  of  moments  to  the  centers  of 
gravity  of  one-half  the  respective  loads.  The  positive 

W  l  Wl 

moment  is  equal  to  — X-  = -  and  the  negative  moment 

2  4  8' 


14 


HEAVY  FOUNDATIONS 


§38 


,  4  Wk/x  Wx 

is  equal  to  — X-  = - ; 

2  4  8 


then  the  bending  moment  M  equals 

Wl  Wx 
8  8 


or 


W 

M=—(l-x) 

8 


The  method  of  obtaining  the  bending  moment  as  explained 
by  this  formula  may  be  stated  as  follows: 


Rule. —  The  bending  moment  on  any  tier  of  steel  beams  in  the 
grillage  footing  is  equal  to  one-eighth  of  the  entire  weight  on 
the  column  multiplied  by  the  difference  between  the  length  of 
the  steel  beams  considered  and  the  width  of  the  steel-beam  grillage , 
or  the  cast-iron  base  above. 


Example. — According  to  the  formula,  what  size  beams  will  be 
required  in  the  steel-beam  grillage  footing  shown  in  Fig.  9,  considering 
a  safe  unit  fiber  stress  of  15,000  pounds,  provided  the  load,  as  in  the 
previous  example,  is  equal  to  400,000  pounds? 


Solution. — In  the  upper  tier  of  beams,  the  distance  l  in  this  case 
is  equal  to  their  length,  or  142  in.,  while  the  distance  x  is  equal  to  the 
width  of  the  base  plate,  or  30  in.  By  substituting  these  values, 
together  with  the  total  load  W,  or  400,000  lb.,  in  the  formula, 
400,000 

M  =  — - —  X  (142  —  30)  =  5,600,000  in. -lb.  The  bending  moment  on 

8 

the  beams  in  the  second  tier,  by  the  same  formula,  is  equal  to 
400,000 

M— - X  (123  —  51)  =  3,600,000  in. -lb.  The  section  modulus  for 

8 

each  beam  may  then  be  determined  by  applying  formula  1,  Art.  8,  or 
M 

S  = — .  On  substituting  the  respective  values  in  this  formula,  the 
s  n 


section  modulus  for  the  upper  tier  is  equal  to 
while  for  the  lower  tier  the  section  modulus  equals 


5,600,000 

15,000X6 

3,600,000 

15,000  X  14 


62.22, 

17.14. 


From  a  table  of  the  properties  of  beam  sections,  a  15-in.  I  beam  weigh¬ 
ing  50  lb.  will  be  found  most  economical  for  the  upper  tier,  while  for  the 
lower  tier  a  9-in.  I  beam  weighing  21 1  lb.  is  suitable.  Ans. 


It  will  be  observed  that  by  this  method  of  calculation 
heavier  beams  are  required,  and  the  formula  consequently 


TABLE  I 

SAFE  LOAD  ON  ONE  BEAM,  IN  TONS  OF  3,000  POUNDS 


Beam 


Unloaded  Length  of  Beam,  l—x,  in  Inches 


Depth  in 
Inches 

Weight  in 
Pounds 
per  Foot 

36 

48 

60 

4 

72 

84 

96 

108 

120 

132 

144 

156 

168 

180 

24 

IOO 

I5I.I 

132.2 

H7-5 

105-7 

96.1 

88.1 

81.3 

75-5 

70-5 

24 

95 

146.6 

128.3 

114.0 

102.6 

93-3 

85.5 

78.9 

73-3 

68.4 

24 

90 

142. I 

124.3 

no. 5 

99-5 

90.4 

82.9 

76.5 

71. 1 

66.3 

24 

85 

137-7 

120.4 

107. 1 

96.4 

87.6 

80.3 

74-i 

68.8 

64  2 

24 

80 

132.5 

H5-9 

103. 1 

92.6 

84.3 

77-3 

71-3 

66.3 

61.8 

20 

75 

112.8 

96.9 

84.6 

75-2 

67.7 

61.4 

56.4 

52.1 

48.3 

45-1 

20 

70 

108.4 

93-0 

81.3 

72.3 

65.1 

59-2 

54-2 

50.1 

46.5 

43-4 

20 

65 

104.0 

89.1 

78.0 

69.3 

62.4 

56.7 

52.0 

48.0 

44.6 

41.6 

18 

70 

109.2 

91.0 

78.0 

68.3 

60.7 

54-6 

49-7 

45-5 

42.0 

39-o 

36.4 

18 

65 

104.4 

87.0 

74.6 

65-3 

58.0 

52.2 

47-5 

43-5 

40.2 

37-3 

34-8 

18 

60 

99-7 

83.1 

71.2 

62.3 

55-4 

49-9 

45-3 

41.6 

38.4 

35-6 

33-2 

18 

55 

94-3 

78.6 

67.4 

58.9 

52-4 

47.1 

42.9 

39-3 

36.3 

33-7 

31-4 

15 

60 

95-7 

76.7 

63.8 

54-7 

47-9 

42.6 

38.3 

34-8 

3i-9 

29-5 

27.4 

25-5 

15 

55 

90.8 

72.6 

60.5 

51-9 

45-4 

40.4 

36.3 

33-2 

30.3 

27-9 

25-9 

24.2 

15 

50 

86.0 

68.8 

57-3 

49-1 

43-0 

38.2 

34-4 

31-3 

28.7 

26.5 

24.6 

22.9 

IS 

45 

81. 1 

64.9 

54-o 

46.3 

40.5 

36.0 

32-4 

29-5 

27.0 

24.9 

23.2 

21.6 

IS 

42 

78.5 

62.8 

52.4 

44.9 

39-3 

34-9 

31-4 

28.6 

26.2 

24.2 

22.4 

20.9 

12 

40 

72.9 

54-7 

43-7 

36.4 

31-2 

27-3 

24-3 

21.9 

19.9 

18.2 

16.8 

15-6 

14.6 

12 

35 

67.6 

50.7 

40.5 

33-8 

29.0 

25-3 

22.5 

20.2 

18.4 

16.9 

15-6 

14.5 

13-5 

12 

3ii 

64.0 

48.0 

38.4 

32.0 

27.4 

24.0 

21.3 

I9.2 

17.4 

16.0 

14.8 

13-7 

12.8 

IO 

40 

56.4 

42.3 

33-8 

28.2 

24.2 

21. 1 

18.8 

16.9 

15-4 

I4-I 

130 

12. 1 

II-3 

IO 

35 

52.1 

39-1 

31.3 

26.0 

22.3 

19-5 

17.4 

156 

14.2 

13-0 

12.0 

II. 2 

10.4 

IO 

30 

47.6 

35-7 

28.6 

238 

20.4 

17.9 

15-9 

M-3 

130 

11.9 

II.O 

10.2 

9-5 

IO 

25 

43-4 

32.5 

26.0 

21.7 

18.6 

16.3 

M-5 

13-0 

11.8 

10.8 

10. 1 

9-3 

8-7 

9 

35 

44-1 

33-1 

26.5 

22.0 

18.9 

16.5 

14-7 

13.2 

12.0 

II.O 

10.2 

9-5 

8.8 

9 

30 

40.2 

30.1 

24.1 

20.1 

17.2 

IS- 1 

13-4 

12. 1 

II.O 

10.0 

9-3 

8.6 

8.0 

9 

25 

36.3 

27.2 

21.8 

1S.1 

15-5 

13-6 

12. 1 

IO.9 

9.9 

9.1 

8,4 

7-8 

7-3 

9 

21* 

33-6 

25.2 

20.2 

16.8 

14.4 

12.6 

n. 2 

10. 1 

9.2 

8.4 

7-8 

7.2 

6.7 

8 

25* 

30.2 

22.7 

18.1 

151 

13.0 

H.3 

10. 1 

9.1 

8.2 

7.6 

7.0 

6-5 

6.0 

8 

22I 

28.4 

213 

17. 1 

14.2 

12.2 

10.7 

9-5 

8.5 

7-8 

7-1 

6.6 

6.1 

5-7 

8 

20* 

26.7 

20.0 

16.0 

13-3 

11.4 

10.0 

8.9 

8.0 

7-3 

6.7 

6.2 

5-7 

5-3 

8 

18 

25-3 

18.9 

15-2 

12.6 

10.8 

9-5 

8.4 

7.6 

6.9 

6.3 

5.8 

5-4 

5-i 

7 

20 

215 

l6. 1 

12.9 

10.8 

9.2 

8.1 

7.2 

6.5 

5-9 

5-4 

5-o 

4.6 

4-3 

7 

17* 

19.9 

14-9 

12.0 

10.0 

8-5 

7-5 

6.6 

6.0 

5-4 

5-o 

4.6 

4-3 

4.0 

7 

15 

18.5 

13-9 

11. 1 

9.2 

7-9 

6.9 

6.2 

5-6 

5-0 

4.6 

4-3 

4.0 

3-7 

6 

I7* 

155 

11.6 

9-3 

7-7 

6.6 

5-8 

5-2 

4.6 

4.2 

3-9 

3-6 

3-3 

3-1 

6 

i4* 

14.2 

10.7 

8-5 

7-i 

6.1 

5-3 

4-7 

4-3 

3-9 

3-6 

3-3 

3-0 

2.8 

6 

12* 

130 

9-7 

7-8 

6-5 

5-6 

4.9 

4-3 

3-9 

3-5 

3-2 

3-0 

2.8 

2.6 

5 

m3 

10.8 

8.1 

6.5 

5-4 

4-7 

4.1 

3-6 

3-3 

3-0 

2-7 

2-5 

5 

12* 

9.6 

7.2 

5-8 

4.8 

4.1 

3-6 

3-2 

2.9 

2.6 

2.4 

2.2 

5 

91 

8-5 

6.4 

5.1 

4-3 

3-7 

3-2 

2.8 

2.6 

2.3 

2.1 

2.0 

4 

10* 

6.4 

4.8 

3-8 

3-2 

2.7 

2.4 

2.1 

4 

9* 

6.0 

4-5 

3-6 

3-0 

2.6 

2.3 

2.0 

4 

8* 

5-7 

4-3 

3-4 

2.8 

2.4 

2.1 

1.9 

4 

7* 

5-3 

4.0 

3-2 

2.7 

2.3 

2.0 

i.s 

3 

7* 

3-4 

2-5 

2.0 

3 

6* 

3-2 

2.4 

2.0 

3 

5* 

3-0 

2.3 

1.8 

15 


16 


HEAVY  FOUNDATIONS 


§38 

gives  safer  results.  The  principles  on  which  the  formula  is 
based  are  theoretically  correct,  whereas,  in  the  other  method 
they  were  not,  so  that  the  more  conservative  rule  should  be 
used.  Both  methods  are  given  here,  as  they  are  both  used  in 
general  practice  in  the  design  of  these  footings. 


10.  For  convenience  in  figuring  the  strength  of  steel 
beams  in  grillage  footings,  Table  I  is  given.  This  table  gives 
the  safe  load  on  a  single  beam  in  tons  of  2,000  pounds  when 


< - 

- / 

4-0 

l 

9-0  ‘ 
3-'0' 

X 

- -  >. 

/ 

. 

I 

 1 

J 

1 

1 

1 

{ 

• 

r 

.  ...  . 

\-f-r 

FT 

i 

ZJ 

11  1  1  ~1 

■  '•  ■  - - - 

1  i  Is 

i 

i 

1 

!  1  1  1  1 

— 1 - 1 — i - 1 — 

l 

1 

1  1 - 1 - 1 - 1 - 

1  1 

i 

— 1 

i — i — t — r — i— 

ill 

1 

i 

1 

i  ...  , 

1 

r  i  r 

Fig.  10 


a  safe  unit  fiber  stress  of  16,000  pounds  is  assumed.  In 
applying  the  table,  it  is  necessary  to  determine  the  value  of 
l  —  Xy  or  the  difference  between  the  length  of  the  steel  beams 
beneath  and  the  width  of  the  steel-beam  grillage  or  the 
cast-iron  base  above,  as  shown  in  Fig.  10.  When  the  required 
value  of  l  —  x  is  not  given  in  the  table,  the  value  next  higher 
should  be  taken.  It  is  also  necessary  to  determine  the  total 
uniform  load  on  each  beam  in  the  tier  under  consideration; 
this  may  be  found  by  dividing  the  total  load  on  the  footing 


§38 


HEAVY  FOUNDATIONS 


17 


by  the  number  of  beams.  In  the  column  giving  the  existing 
value  of  l  —  x,  select  the  value  nearest  to  the  uniformly 
distributed  load,  in  tons,  on  the  beam  and  by  referring  to 
the  columns  headed  Depth  and  Weight,  the  size  of  the  steel 
beam  for  the  tier  will  be  found. 

For  example,  Fig.  10  shows  a  diagrammatic  plan  of  a 
three-tier,  steel-beam,  grillage  footing..  The  load  on  the 
column  is  350,000  pounds,  or  175  tons,  so  that  the  load  on 
each  beam  in  the  several  tiers  is  as  follows: 


Top  tier  =  175^  5  =  35  tons 
Middle  tier  =175^  8  =  21.875  tons 
Bottom  tier=  175 -f- 10=  17.5  tons 


The  values  oi  l  —  x  for  the  several  tiers  may  be  determined 
thus: 

Top  tier  ’=  9  — 3  =  G  feet  =  72  inches 
Middle  tier  =10  —  3  =  7  feet  =  84  inches 
Bottom  tier  =14  —  9  =  5  feet  =  60  inches 


Then,  referring  to  Table  I,  for  the  first  tier  of  beams, 
under  the  column  headed  72,  it  will  be  found  that  a  12-inch 
40-pound  beam  is  the  lightest  that  will  support  the  required 
load  and  that  for  the  middle  tier  of  beams,  under  the  column 
headed  84,  a  12-inch  31^-pound  beam  will  be  the  most 
economical,  while  for  the  bottom  tier  of  beams,  under  the 
column  headed  GO,  the  most  economical  beam  will  be  the 
9-inch  21^-pound  beam. 

In  calculating  the  values  given  in  this  table,  a  formula 
evolved  from  the  elementary  equation  M  =  Mx  has  been 
used.  M1  equals  the  resisting  moment  or  5  s,  while  M  equals 
the  bending  moment,  which,  according  to  the  formula  of 
.  W 

Art.  9,  is  —  (l  —  x).  Substituting  these  values  in  the  equation 
8 

W 

M  =  Mt  gives  5^  =  — (l  —  x),  and  transposing,  the  equation 


,  5  5  l  —  x 

becomes  —  = - 

W  8 


In  this  equation,  5  is  the  ultimate  unit 


fiber  stress,  and  by  dividing  by  the  factor  of  safety,  the 
211—26 


18 


HEAVY  FOUNDATIONS 


§38 


safe  unit  stress  is  obtained,  which,  according  to  the  table, 
is  equal  to  16,000  pounds.  Substituting  this  value,  the 

TABLE  II 

DEPTH,  WEIGHT,  AND  SECTION  MODULUS  OF  STANDARD 

I  BEAMS 


Depth 
of  Beam 

Inches 

Weight 
per  Foot 

Pounds 

' 

Section 

Modulus 

Inches3 

Depth 
of  Beam 

Inches 

Weight 
per  Foot 

Pounds 

1 

Section 

Modulus 

Inches3 

3 

5-5° 

i-7 

10 

25.00 

24.4 

3 

6.50 

1.8 

10 

30.00 

26.8 

3 

7-5° 

1.9 

10 

35-oo 

29-3 

4 

7-5o 

3-o 

10 

40.00 

31-7 

4 

8.5° 

3-2 

1 2 

3i-5o 

36.0 

4 

9-5° 

3-4 

12 

35-0° 

38.0 

4 

10.50 

3-6 

1 2 

40.00 

41.0 

5 

9-75 

4.8 

*5 

42.00 

.  58.9 

5 

12.25 

5-4 

!5 

45.00 

60.8 

5 

14-75 

6. 1 

!5 

50.00 

64-5 

6 

12.25 

7-3 

J5 

55-oo 

68.1 

6 

M-75 

8.0 

T5 

60.00 

71.8 

6 

17-25 

8.7 

18 

55-oo 

88.4 

7 

15.00 

10.4 

18 

60.00 

93-5 

7 

I7-5° 

1 1.2 

18 

65.00 

97-9 

7 

20.00 

1 2. 1 

18 

70.00 

102.4 

8 

18.00 

14.2 

20 

65.00 

1 17.0 

8 

20.25 

15.0 

20 

70.00 

122.0 

8 

22.75 

16.0 

20 

75.00 

1 26.9 

8 

25-25 

17.0 

24 

80.00 

T73-9 

9 

21.50 

18.9 

24 

85.00 

180.7 

9 

25.00 

20.4 

24 

90.00 

186.5 

9 

30.00 

22.6 

24 

95.00 

192.4 

9 

35-oo 

24.8 

24 

100.00 

r98.3 

r  ,  .  16,000  5  l  —  x  . 

formula  becomes - = - .  W  is  m  pounds,  while, 

W  8 

according  to  the  table,  it  should  be  in  tons;  therefore,  by 


HEAVY  FOUNDATIONS 


19 


§  38 


dividing  the  left-hand  member  of  the  equation  by  2,000, 

8  vS*  /  % 

the  formula  is  changed  to  - =  - — and  by  transposi¬ 

n'  8 

64  5 

tion,  W  =  — — ,  which  is  the  formula  by  which  the  values 
l  —  x 

in  the  table  are  calculated. 

11.  Table  II  is  given  for  reference.  It  contains  the 
sizes,  weights,  and  section  moduli  of  standard  I-beam  sections, 
and  may  be  used  to  find  the  section  moduli  of  beams  of  various 
sizes,  as  required  by  certain  of  the  preceding  formulas. 


EXAMPLES  FOR  PRACTICE 

1.  A  grillage  footing  is  composed  of  two  tiers  of  steel  beams;  and 
the  column  base,  which  is  30  inches  wide,  supports  a  load  of  275,000 
pounds.  The  steel  beams  in  the  first  tier  are  five  in  number,  the 
tier  is  42  inches  in  width,  measuring  between  the  outside  edges  of  the 
flanges  of  the  outside  beams,  and  the  length  of  the  beams  in  this  tier 
is  150  inches.  The  number  of  beams  in  the  bottom  tier  is  fifteen  and 
their  length  is  also  150  inches.  Provided  that  an  allowable  unit  fiber 
stress  of  18,000  pounds  is  assumed  and  that  the  formula  of  Art.  9  is 
employed,  what  will  be  the  economical  sizes  of  the  beams  in  both  tiers? 

/Upper  tier,  15-in.  42-lb.  beams 


Ans. 


l  Lower  tier,  8-in.  18-lb.  beams 


2.  What  will  be  the  sizes  of  the  beams  required  in  example  1  if 


the  formula  of  Art.  7  is  used? 


f  Upper  tier,  12-in.  35-lb.  beams 
‘  l  Bottom  tier,  7-in.  15-lb.  beams 


3.  Determine  by  means  of  Table  I,  without  interpolating,  the 
economic  sizes  of  steel  beams  required  for  a  grillage  footing  composed 
of  three  tiers  of  steel  beams.  The  bottom  tier  is  12  feet  6  inches  long 
and  10  feet  wide,  the  intermediate  tier  has  a  length  equal  to  the  width 
of  the  bottom  tier  and  a  width  of  6  feet,  and  the  top  tier  extends 
across  the  intermediate  tier  and  is  4  feet  6  inches  wide.  The  cast-iron 
base  is  rectangular  in  plan  and  is  equal  in  length  to  the  width  of  the  top 
tier  and  is  3  feet  wide.  Six  beams  compose  the  top  tier,  while  in  the 
intermediate  and  bottom  tiers  there  are  nine  and  twelve,  respectively. 
The  load  on  the  footing  is  from  a  principal  column  and  amounts  to 
320  tons.  Bottom  tier,  12-in.  31^-lb.  beams 

Ans.<  Intermediate  tier,  12-in.  40-lb.  beams 
■  Top  tier,  10-in.  40-lb.  beams 


20 


HEAVY  FOUNDATIONS 


§38 


COMPOUND  FOOTINGS 


RECTANGULAR  FOOTINGS 

12.  A  compound  footing;  is  a  footing  that  supports 
two  or  more  loads,  as,  for  example,  the  loads  from  two  or 
more  separate  columns.  Compound  footings  may  be  divided 
into  two  classes,  namely,  those  which  are  square  or  rectam 
gular  and  those  which  are  not  so  shaped.  The  latter  are 
usually  fan-shaped.  The  square  or  rectangular  footings 
will  be  discussed  first. 


Fig.  11 


13.  Location  of  Center  of  Gravity. — The  first  point 
of  consideration  is  to  distribute  the  area  of  the  footing  in 
the  proper  manner.  The  requirements  are  two:  (1)  that 
the  unit  pressure  on  the  soil  shall  not  be  excessive,  and 
(2)  that  it  shall  be  uniform.  When  the  load  and  the  unit 
bearing  value  of  the  soil  are  known,  the  area  of  the  footing 
may  be  obtained  by  dividing  the  former  by  the  latter.  But 


§38 


HEAVY  FOUNDATIONS 


21 


the  second  requirement,  namely,  the  necessity  of  having  the 
pressure  uniform,  must  not  be  overlooked;  if  it  is  neglected, 
the  footing  will  settle  unevenly  and  the  building  is, liable  to 
be  cracked,  twisted,  or  perhaps  even  destroyed.  When  only 
one  column  rests  on  the  footing,  all  that  is  necessary  is  to 
have  the  center  line  of  the  column  directly  over  the  center  of 
gravity  of  the  footing  area.  When  two  or  more  columns 
rest  on  one  footing,  the  center  of  gravity  of  the  combined 
loads  must  coincide  with  the  center  of  gravity  of  the  foot¬ 
ing  area. 


Fig.  12 

14.  In  order  to  illustrate  the  foregoing  principle,  the 
following  problem  is  given:  Three  columns,  as  shown  in 
Fig.  11,  rest  on  one  footing,  and  they  all  carry  the  loads 
shown.  The  soil  will  carry  safely  1^-  tons  per  square  foot. 
Proportion  the  area  of  the  footing. 

First,  the  area  of  the  entire  footing  may  be  obtained. 
The  total  load  to  be  supported  is  42  +  96  +  62  =  200  tons. 
Since  the  soil  can  safely  sustain  1  \  tons  per  square  foot,  the 
area  of  the  footing  must  be  200  1 4  =  1 33 J  square  feet. 

Either  the  width  or  the  length  of  the  footing  may  be  assumed, 
although  in  actual  design,  the  conditions  encountered  will 


22 


HEAVY  FOUNDATIONS 


§38 


usually  limit  one  of  these  dimensions.  In  the  case  under 
consideration,  assume  that  the  footing  can  be  only  4  feet 
wide.  Then,  the  length  of  the  footing  will  be  133^  -s-  4  =  33  feet 
4  inches. 

The  next  step  is  to  locate  the  footing  under  the  columns 
so  as  to  transmit  the  load  uniformly  to  the  soil.  First, 
the  center  of  gravity,  or  center  of  action,  of  the  three  column 
loads  must  be  found.  To  do  this,  take  moments,  for  instance, 
about  the  center  line  of  the  left-hand  column.  The  location 
of  the  center  of  gravity  is  found  thus: 

Load  Moment  Arm  Moment 


Column  1 .  42  0  0 

Column  2 .  96  12  1,152 

Column  3 .  62  21  1,302 

Total . 200  2,454 


The  distance  from  the  center  line  of  the  left-hand  column 
to  the  center  of  action  of  the  combined  loads  is  therefore 
2,454-r-200=12.27  feet.  This  point  is  then  the  center  of 
gravity  of  the  footing  area  also.  The  footing  is  placed  as 
shown  in  Fig.  12. 

15.  Footings  With  Two  Columns. — After  having 
determined  the  location  and  area  of  a  footing,  the  strength 
of  the  steel  beams  in  it  may  be  investigated. 


d 

Fig.  13 


In  order  to  determine  the  correct  size  of  beams  to  use  in  a 
footing,  simply  find  the  maximum  bending  moment  to  which 
they  will  be  subjected  and  then  proportion  the  beams 
to  withstand  this  moment.  The  maximum  moment,  as 
explained  in  Forces  Acting  on  Beams ,  occurs  at  the  point  of 
zero  shear.  In  most  footings  with  several  columns  resting 
on  them,  there  are  two  or  more  points  of  zero  shear,  and 
each  of  these  must  be  investigated. 


§38 


HEAVY  FOUNDATIONS 


23 


16.  As  a  typical  example  of  a  footing  supporting  two 
columns,  find  the  maximum  bending  moment  in  the  beams  d, 
Fig.  13.  It  is  assumed  that  the  loads  on  both  columns  are 
known  and  that  the  area  of  the  footing  is  properly  propor¬ 
tioned  and  properly  distributed  under  these  columns.  The 
condition  of  loading  to  which  the  beams  d  in  the  footing  are 
subjected  is  illustrated  diagrammatically  in  Fig.  14.  The 
column  loads  are  Wl  and  W2,  and  by  means  of  their  bases 


Fig.  14 


they  are  distributed  over  the  respective  lengths  xt  and  x2  of  the 
beams  d.  The  load  per  linear  foot  that  these  columns  exert  is 

W  Wo 

called  wx  and  w2,  and  equals  — -  and  — -,  respectively.  The 

total  reaction  of  the  earth  on  the  footing  is,  of  course,  equal  to 
W x  T  W 2,  and  the  pressure  per  linear  foot  of  foundation, 

Wt  +  W2 


or  p,  is  equal  to 


l 


First,  the  points  of  no  shear  must  be  found.  It  may  be 
taken  as  a  general  rule— although  there  may  be  exceptions 


yx-54- 


ini 


y^&4' 


X2  =36- 


ini 


fO  Beams 


_  .  /  _  // 
-£2-0 


Fig.  15 


■ — that  there  is  one  point  of  no  shear  under  each  column  load 
and  one  point  of  no  shear  between  each  two  columns.  The 
locations  of  these  points  are  to  be  found,  and  they  are  assumed 


24 


HEAVY  FOUNDATIONS 


§38 


to  be  at  distances  from  the  left-hand  end  of  the  grillage 
indicated  by  llf  l2,  and  /3.  The  formulas  that  give  values  for 
4,  /2,  and  4  are  based  on  principles  given  in  Forces  Acting 
on  Beams ,  and  are  as  follows: 


hp-wi(h  Vi),  or  k-  y'  ' 

w1  —  p 

(1) 

7  Tjr  ,  Wt 

4  p  =  w  1,  or  4  =  — 1 

P 

(2) 

hP=wl+[l3-  (. v, + + y2y]w2 

or 

p-W  2 

(3) 

After  these  three  values  have  been  found,  the  bending 
moment  at  these  three  points  may  be  determined  by  the 
following  formulas: 

M  _Ph 2  ^(/,-y.)2 
1  2  2 

M2=^-W^l2-yi-^  (5) 

2/  2  '  ' 

These  formulas  are  also  obtained  by  the  principles  given  in 
Forces  Acting  on  Beams. 


pi 2  / 


17.  As  an  example  of  the  foregoing  principles,  determine 
the  most  economical  I  beams  that  may  be  used  for  the  bottom 
tier  of  the  grillage  footing  shown  in  Fig.  15,  provided  that 
there  are  ten  beams  in  the  tier  and  that  a  safe  unit  stress  of 
18,000  pounds  is  assumed.  The  load  from  each  super¬ 
imposed  column  is  375,000  pounds.  All  dimensions  must  be 
put  either  in  feet  or  in  inches.  In  this  case,  it  will  be  simpler 
to  use  inches,  because  the  section  modulus  is  given  in  the 
tables  in  inches.  Thus, 


/  =  22  X  12  =  264  inches ;  p  = 


375,000  +  375,000 


2,840** 


264 


§38 


HEAVY  FOUNDATIONS 


25 


say  2,841,  pounds;  ^  =  375,000-^-36=10,417  pounds,  about; 
and  w2  equals  the  same  amount  as  wv 

Substituting  the  correct  values  in  the  formulas  1,  2,  and  3, 
Art.  1G, 


54X10,417 

10,417-2,841 


=  74.25  inches 


375,000 

2,84f 


=  132.00  inches 


375,000  -  (54  +  36  +  84)  X  10,417 
2,841-10,417 


=  189.75  inches 


Now  that  the  values  of  lv  /2,  and  /3  have  been  found,  the 
moments  of  the  loads  at  these  points  may  be  determined 
according  to  formulas  4,  5,  and  6,  Art.  1G. 

Substituting  the  proper  values  in  these  formulas, 

_  2,841  X  74. 252  10,417  X  (74.25 -  54)2 

1  2  2 

=  5,695,494.75  inch-pounds 

o  041  v/ 1 092 

M2  =  »  -  375,000  X  (1 32 -  54  - *f) 

2 

=  2,250,792  inch-pounds 

M3  =  2,841  X9! 89,752  -  375,000  X  (189.75  -  54  - 

_10,417X[189.75-(54±36-f84)]^5i696|90775 

2 

inch-pounds 


If  the  values  of  p  and  lv  l2,  and  l3  had  been  carried  to  a 
sufficient  number  of  decimals,  Mx  and  M3  would  have  been 
alike.  However,  both  are  larger  than  M2;  therefore,  in  this 
case,  the  maximum  bending  moment  occurs  under  the  loads 
and  not  between  them.  This  maximum  moment  may  be 
taken  at  5,700,000  inch-pounds.  Since  there  are  ten  beams 
in  thegrillage,  each  beam  must  sustain  5,700,000 -r- 10  =  570,- 
000  inch-pounds.  With  a  fiber  stress  of  18,000  pounds,  the 


26 


HEAVY  FOUNDATIONS 


§38 


required  section  modulus  is  570,000  -s- 18,000  =  31.67.  Refer¬ 
ring  to  Table  II,  either  a  10-inch  40-pound  beam  or  a  12-inch 
3 Impound  beam  may  be  used.  As  the  latter  is  both  stronger 
and  lighter,  it  is  preferable. 


18.  As  a  complete  example  of  the  design  of  a  footing 
supporting  two  column  loads,  the  following  problem  is 
proposed:  Design  a  footing  to  support  two  columns  on  a 
soil  that  can  sustain  safely  only  2  tons  per  square  foot.  The 
columns  are  9  feet  apart,  center  to  center.  One  supports 
90  tons,  and  the  other  111  tons. 

The  first  step  is  to  find  the  total  area  of  the  footing.  The 
total  load  is  201  tons.  The  required  area  is  therefore  201^2 
=  100.5  square  feet.  In  order  to  make  the  example  more 
interesting,  let  it  be  assumed  that  on  account  of  the  special 
difficulties  encountered  on  this  particular  job,  the  footing 
can  be  only  6  feet  6  inches  wide;  then  it  will  be  100.5 -h  6.5 
=  15.46  feet  long,  or  say  15  feet  6  inches. 

Next,  the  center  of  gravity  of  the  footing  must  be  found. 
This  may  be  done  by  taking  moments  about  the  column 
that  supports  the  90-ton  load.  Thus: 

Load  Moment  Arm  Moment 


90  0 

111  9 

Total,  201 


0 

999 

999 


The  distance  of  the  center  of  gravity  from  the  column 
supporting  90  tons  is  therefore  999 -i- 201  =  4.97,  say  5  feet. 

It  is  next  necessary  to  know  the  size  of  the  base  of  the 
columns.  These  bases  would  be  known  if  the  columns  were 
designed.  Let  it  be  assumed  in  this  case  that  the  bases  are 
each  2  feet  square.  The  grillage  may  be  considered  to  consist 
of  two  tiers  of  beams,  the  bottom  one  of  which  is  15  feet 
6  inches  long  and  6  feet  6  inches  wide.  The  top  tier  is  in 
two  parts,  one  under  each  column.  Each  part  is  6  feet  6  inches 
long  and  2  feet  wide.  It  may  be  assumed  that  each  part  of 
the  top  grillage  contains  four  beams,  and  that  the  bottom 
grillage  contains  twelve  beams.  The  footing  of  the  correct 
proportions  is  shown  in  Fig.  16.  The  beams,  for  convenience 


HEAVY  FOUNDATIONS 


27 


§38 


in  illustrating,  are  extended  to  the  end  of  the  concrete.  In 
actual  practice,  they  are  stopped  short,  and  the  ends  are 
covered  with  an  inch  or  so  of  concrete,  to  protect  them 
from  rust. 

The  long  beams  are  the  first  ones  to  be  investigated,  and  lv 

/2,  and  l3  must  be  found.  From  Fig.  16  the  following  quantities, 

A  „  (90 +  1 11)  X  2,000 

in  pounds  and  inches,  may  be  obtained :  p  =  - - - — — — 

186 

on  v  o  non 

=  2,161.29,  say  2,161,  pounds;  ivx  — - 1 —  =  7,500  pounds; 


Fig.  16 

w2  =  ^ P  =  9,250  pounds;  ^  =  21  inches;  ^  =  24  inches; 
•24 

y2  =  84  inches;  and  :r2=24  inches. 

Substituting  these  values  in  formulas  1 ,  2,  and  3,  Art.  16, 


21X7,500 

7,500-2,161 


29.50  inches 


90  X  2,000  =  g3  29  inches 
2,161 


28 


HEAVY  FOUNDATIONS 


§38 


4  = 


90  X  2,000  -  (21  +  24  +  84)  X  9,250 


=  142.93  inches 


2,161-9,250 

After  lv  /2,  and  l3  have  been  found,  Mx,  M2,  and  M3  may 
be  found  by  formulas  4,  5,  and  6,  Art.  16.  Substituting 
the  correct  values, 

2,161  X  29. 52  7,500  X  (29.5  — 21)2 


2  2 
=  669,367.625  inch-pounds 


M2  = 


2,161  X83.292 


90  X  2,000  X  (83.29  -  21  -  Y) 


=  —1,556,529.35995  inch-pounds 


M3  = 


2,161  X142.932 


90  X  2,000  X  (142.93  -  21  -  Y) 


9,250[  142.93  -  (21  +  24  +  84) ]2 


=  + 1,388,660.52195  inch-pounds 

It  is  evident  that  the  maximum  bending  moment  is  the 
negative  one  of  approximately  —1,556,529  inch-pounds  and 
is  between  the  two  columns.  As  there  are  twelve  beams 
in  the  grillage,  each  beam  must  resist  1,556,529  4- 12=  129,711 
inch-pounds,  approximately.  If  the  allowable  unit  stress 
is  16,000  pounds,  the  required  section  modulus  will  be  129,711 
-r- 16,000  =  8.11.  Referring  to  Table  II,  it  will  be  found  that 
either  a  6-inch  17.25-pound  or  a  7-inch  15-pound  beam  will  be 
strong  enough.  As  the  latter  is  the  lighter,  it  will  be  used. 

The  next  step  is  to  design  the  beams  in  the  upper  grillage. 
The  beams  under  each  separate  column  are  designed  as  the 
beams  of  a  footing  supporting  only  one  column,  as  they  are 
under  the  same  conditions  of  stress.  As  the  columns  carry 
different  loads,  the  beams  under  them  will  be  of  different 
sizes.  The  column  carrying  111  tons  will  be  considered 
first.  To  design  the  beams  under  it,  the  formula  of  Art.  9 
is  used.  Here,  w  =  111 X 2,000  =  222,000  pounds;  /  =  6  feet 
6  inches  =  78  inches;  and  #  =  24  inches.  Therefore, 

222  000 

M  = - — - X  (78  -  24)  =  1 ,498,500  inch-pounds 


8 


§38 


HEAVY  FOUNDATIONS 


29 


As  there  are  four  beams,  each  beam  must  resist  1,498,500 
-.-4  =  374,625  inch-pounds.  With  a  safe  unit  stress  of  16,000 
pounds,  the  required  section  modulus  will  be  374,625 
-v- 16,000  =  23.41.  Referring  to  Table  II,  it  will  be  seen  that 
a  10-inch  25-pound  beam  is  the  lightest  beam  that  is  strong 
enough. 

The  beams  under  the  column  supporting  90  tons  are 
designed  in  the  same  manner.  Thus,  w  =  180,000  pounds; 
/  =  78  inches;  and  x  =  24  inches.  Therefore, 

M  =  x  (78  -  24)  =  1,215,000  inch-pounds 

8 

For  one  beam,  M  — 1,215,000-^4  =  303,750  inch-pounds. 
Therefore,  5  =  303,750  4- 16,000=  18.98 

According  to  Table  II,  a  9-inch  25-pound  beam  must  be 
used. 


19.  Footings  for  Tliree  or  More  Columns. — The 

method  of  procedure  in  designing  a  footing  intended  to  sup¬ 
port  three  or  more  columns  is  similar  to  that  followed  in 
designing  footings  for  the  support  of  two  columns.  First, 
the  footing  must  be  made  large  enough  and  with  its  center 
of  gravity  properly  located.  Next,  the  points  of  no  shear 
must  be  found,  and  then  the  bending  moments  at  these 
points  must  be  obtained  and  the  maximum  moment  selected. 

The  formulas  for  finding  the  points  of  no  shear  and  max¬ 
imum  bending  moment  are  derived  from  the  principles  laid 
down  in  Forces  Acting  on  Beams.  As  will  be  observed, 
the  first  three  formulas  for  both  shear  and  bending  moment 
are  the  same  as  those  previously  given  for  footings  supporting 
two  columns. 

It  is  very  seldom  that  more  than  three  columns  are 
placed  in  a  row  on  one  steel-beam  grillage.  In  such  a  case, 
the  additional  formulas  for  points  of  no  shear  and  bending 
moments  may  be  evolved  from  the  principles  given  in  Forces 
Acting  on  Beams;  or,  the  following  formulas  may  be  used  to 
determine  the  location  of  the  moments  from  the  right-hand 
end  of  the  beam. 


30 


HEAVY  FOUNDATIONS 


§38 


The  formulas  for  the  points  of  no  shear,  using  the  nota¬ 
tion  given  in  Fig.  17,  are  as  follows: 


4  ^  =  Wi(/i-pi),  or  Zj  = 


y  i  wi 


I2  p  IF j,  or  l2 


wt  —  p 

w, 

p 


(1) 


(2) 


4  P = Wt + [4  -  (y, + *1 + y2)K 


or 


4= 


^Fi-(H+^1+T2)W2 


p-w2 


l4p  =  Wt  +  W2,  or  /4  = 


TF1  +  IF2 
P 


(3) 


(4) 


4  />  =  TF1  +  TF2  +  w3[/5-  (h  +  ^  +  ^  +  ^  +  Ts)] 


or 


4= 


IFi  +  1F2  —  (yt  +  aq  +  y2  +  x2  +  y3) 

P~w3 


(5) 


When  the  location  of  the  point  at  which  the  shear  changes 
sign  has  been  determined,  the  bending  moments  can  be 
readily  found,  for  they  are  equal  to  the  algebraic  sum  of 
the  moments  about  the  points  in  question.  With  reference 
to  Fig.  17,  the  formulas  for  the  bending  moments  at  the 
several  points  are  as  follows: 


M,= 


P  42  “',(4-^1): 


(6) 


M3 = til  _  w,  (l,-yt--\- 


(7) 


(8) 


Ph 


X 


1 


—  W2  l4—  +  xx  +  y2  + 


Xn 


(9) 


§38 


HEAVY  FOUNDATIONS 


31 


—  ^2  j^4  -  [y\ + xi + y* + 

wJ/5  -  (y  1 + xt + y2 + *2 + y3)  f  ^  0 

2  ^  ; 


20.  The  formulas  of  Art.  19 
may  be  used  to  find  the  bending 
moment  in  reinf orced-concrete  foot¬ 
ings  as  well  as  in  footings  made  of 
steel  beams.  To  illustrate  the  appli¬ 
cation  of  these  formulas,  the  follow¬ 
ing  problem  will  be  worked  out: 
Proportion  the  steel  beams  in  the 
grillage  foundation  shown  in  Fig.  18 
for  the  greatest  bending  moment. 
The  allowable  unit  stress  is  16,000 
pounds,  and  the  loads  on  the  col¬ 
umns  and  the  general  dimensions 
of  the  footing  are  given  in  the 
figure. 

21.  It  is  first  necessary  to  de¬ 
termine  the  values  of  Zlf  l2,  l3,  etc. ; 
having  these  distances,  which 
locate  the  points  at  which  the 
shear  changes  sign,  the  bending 
moments  at  these  points  may  be 
determined  by  formulas  6  to  10, 
Art.  19,  inclusive,  and  from  this 
data  the  greatest  bending  mo¬ 
ment  is  found  by  inspection  and 
the  beam  proportioned  accor¬ 
dingly.  With  reference  to  the  fig¬ 
ure  and  by  substitution  in  formulas 

1  to  5,  Art.  19,  the  values  of 

* 

llt  etc.  are  found  as  follows: 


32 


HEAVY  FOUNDATIONS 


§38 


k  = 


yxwx  52X5,556 


=  84.16 


wx  —  p  5,556  —  2,123 

^=200i00_0  =  942i 

p  2,123 

,  _Wt—  (yt  +  xt  +  y2)  X  w2  _  200,000  -  (52  -f  36  +  82)  X  7,500 

/ - ■  -  * 


p-w2 


2,123-7,500 


=  199.93 


7  _  Wt  +  W2_  200,000  +  300,000 _ 

l  a - *  ZoO.OZ 

p  2,123 

,  _W1  +  W2-(y1+x1+y2+x2+y3)w3 

p  —  W 3 

200,000  +  300,000  -  (52  +  36  +  82  +  40  +  65)  X  8,333 


=  288.49 


2,123-8,333 

These  values  may  be  substituted  in  formulas  6  to  10, 
Art.  19,  which  will  give  the  bending  moments  at  the  several 
points  as  follows: 

pi?  w^-yj2  2,123X84.16X84.16  ■ 


Mx  = 


2  2 
5,556(84.16- 52)2 


M, 


pl? 


=  4,645,314  inch-pounds 
xx\  2,123X94.21X94.21 


-  200,000  X'(94.21  -  70.00)  =  4,579,369  inch-pounds 
p  42  w /,  ..  wlk- (yi+Xi+yJY 


2,123X199.93X199.93 


-  200,000 X  (199.93 -70) 


7,500X[199.93—  (52  +  36  +  82)  ]2 


=  13,085,014  inch-pounds 


pi, 


X, 


l,  ~  (  >'i  +Xi  1- I2  + 


Xn 


=  2' I23  X  235.52 X  235.52  _  20Q  00Q x  (235  -52 _  70) 


—  300,000 X  (235.52-190)  =  12,121,055  inch-pounds 


33 


211—27 


34 


HEAVY  FOUNDATIONS 


§38 


_  w3[4  -  (m + *1 + y2+x  2 + y3)  f = 

2 


4  —  (^1  +  *1  +  ^2  + 

2,123X288.49X288.49 

9 


-  200,000  X  (288.49  -  70)  -  300,000  X  (288.49  - 100) 

8, 333 X [288.49 -(52  +  36  +  82  +  40  +  65)]2  __ 

—  14.o4 1 ,  # 


inch-pounds 


From  these  calculations  it  will  be  observed  that  the  greatest 
bending  moment  is  at  the  point  M5,  located  under  the  right- 
hand  column.  There  are,  according  to  Fig.  18,  twenty  I  beams 
in  the  grillage,  so  that  the  bending  moment  on  each  I  beam 
will  be  14,341,729-^-20  =  717,086.45,  and  since  the  allowable 
unit  fiber  stress  is  16,000  pounds,  the  required  section  modulus 
for  each  beam  will  equal  717,d86.45  4- 16,000  =  44.818.  From 
Table  II,  it  will  be  observed  that  the  beam  having  the  required 
section  modulus  is  a  15-inch  42-pound  I  beam. 


EXAMPLES  FOR  PRACTICE 


1.  Determine  the  points  of  no  shear,  or  the  points  at  which  the 
greatest  bending  moments  occur,  in  the  grillage  shown  in  Fig.  19  when 
W1  equals  300,000  pounds;  W2,  250,000  pounds;  and  W3,  325,000 
pounds.  The  distances  ylt  xv  y2,  x2,  y3,  and  x3  equal,  respectively, 
58,  40,  80,  3G,  72,  48,  and  the  length  of  the  grillage  equals  33  feet. 

4  =  82.23  in.  =  6  ft.  10£  in. 
4=135.75  in.  =  11  ft.  3f  in. 
Ans.  L=  197.73  in.  =  16  ft.  5f  in. 
4  =  248.87  in.  =  20  ft.  8|  in. 
L  =  303.99  in.  =  25  ft.  4  in. 


Fig.  19 


2.  If  the  values  of  yv  xlf  y2,  x2,  y3,  and  x3  in  Fig.  19  are,  respect¬ 
ively,  equal  to  60,  40,  90,  48,  80,  and  44  inches,  and  the  length  of  the 
bottom  tier  of  beams  is  35  feet  4  inches,  while  the  loads  Wv  W2,  and 


§38 


HEAVY  FOUNDATIONS 


35 


IV 3  are  equal  to  150,  200,  and  175  tons,  in  the  order  named,  how  large 
should  the  beams  be  in  the  lower  tier,  provided  they  are  spaced 
12  inches  from  center  to  center?  The  footing  is  1 1  feet  wide  between 
the  centers  of  outside  beams,  and  the  safe  unit  fiber  stress  is  18,000 
pounds.  Ans.  15-in.  55-lb.  beams 


FAN-SHAPED  FOOTINGS 

22.  Consider  the  case  of  a  footing  that  supports  two 
columns,  one  loaded  with  150  tons  and  one  loaded  with 
15  tons,  when  the  columns  are  10  feet  apart.  Suppose  the 
soil  can  sustain  only  1  ton  per  square  foot.  The  area  of  the 
footing  will  then  be  150  +  15  =  165  square  feet.  If  there 
is  some  obstruction,  say  near  the  column  carrying  15  tons, 
that  limits  the  width  of  the  footing  to  5  feet,  the  footing 
will  be  165 -*-5  =  33  feet  long.  There  are  two  objections  to  a 
footing  of  this  length.  First,  on  account  of  its  length,  there 
will  be  a  very  large  bending  moment,  which  must  be  resisted 
by  heavy  and  expensive  beams,  and,  second,  it  may  interfere 
with  other  foundations  elsewhere  in  the  building. 

Consider  the  case  of  two  columns,  one  supporting  200  tons 
and  one  supporting  30  tons,  when  they  are  10  feet  apart. 
The  soil  can  support  10  tons  per  square  foot.  The  area  of 
the  footing  is  then  (200  +  30)  -r-  10  =  23  square  feet.  Suppose 
the  width  of  the  base  under  the  column  supporting  the  heavier 
load  to  be  such  that  the  footing  must  be  at  least  1  foot  9  inches 
wide;  then,  its  length  will  be  23-f-  If  =  13.14  feet.  The 
distance  of  the  center  of  gravity  from  the  heavier  column 
10  X  30 

must  be - =1.3  feet.  It  can  thus  be  seen  that  the 

200  +  30 

footing,  if  properly  placed,  will  not  reach  under  the  lighter 
column. 

In  cases  like  the  two  just  cited,  rectangular  footings  are 
inconvenient  or  even  impossible.  Therefore,  fan-shaped 
footings  are  employed. 

23 .  Fig.  20  illustrates  two  fan-shaped  footings.  The 
one  shown  in  (a)  is  strengthened  with  steel  beams,  and  the 
one  in  ( b )  is  made  of  reinforced  concrete.  The  method  of 


80  Cor r.  Bars 


Beef /or?  K.K. 


36 


§38 


HEAVY  FOUNDATIONS 


37 


designing  these  two  footings  is  identical,  and  along  the  same 
lines  that  were  followed  with  rectangular  footings.  First, 
the  area  of  the  footing  must  be  made  large  enough  to  carry 
the  required  load.  Then,  the  area  must  be  so  located  that 
its  center  of  gravity  will  coincide  with  the  center  of  gravity 
of  the  loads.  The  maximum  bending  moment  must  next 
be  found  and  a  sufficiently  strong  beam  grillage  designed; 
or,  in  the  case  of  reinforced  concrete,  sufficient  steel  reinforce¬ 
ment  must  be  provided. 


On  account  of  the  shape  of  the  footing,  its  center  of  gravity 
is  not  so  easy  to  find  as  that  of  rectangular  footings,  and, 
usually,  the  shape  of  the  footing  has  to  be  assumed  and 
then  investigated  to  see  whether  or  not  the  center  of  gravity 
comes  in  the  correct  place.  Of  course,  the  footing  may  be 
shifted  a  little,  but  not  so  much  as  was  done  with  a  rectan¬ 
gular  footing. 

24.  Shape  of  Footing. — Various  shapes  of  fan  foot¬ 
ings  are  in  use.  A  plan  view  of  four  styles  is  shown 


38 


HEAVY  FOUNDATIONS 


§38 


in  Fig.  21.  The  shape  shown  in  (a)  is  used  most,  for  two 
reasons;  in  the  first  place,  the  steel  beams  fit  in  it  better 
because  there  are  no  comers,  and,  second,  the  formulas 
for  the  points  of  no  shear  and  bending  moment  are  simpler 
than  with  the  other  shapes.  To  find  the  bending  moments 


of  footings  shaped  as  shown  in  ( b ),  (c),  and  (d),  the  simplest 
way  is  to  lay  the  footing  out  as  a  beam;  that  is,  lay  out  its 
load  diagram,  its  shear  diagram,  and  its  bending-moment 
diagram,  as  was  explained  in  Forces  Acting  on  Beams.  There 
are  no  general  formulas  that  will  fit  all  these  cases.  For  the 
reasons  mentioned,  the  shape  of  footing  generally  used  is 


§38 


HEAVY  FOUNDATIONS 


39 


that  shown  in  (a).  This  shape,  therefore,  is  the  only  one 
that  will  be  considered  in  this  Section. 


25.  Method  of  Design. — As  previously  stated,  the 
theory  of  designing  a  fan-shaped  footing  is  the  same  as  that 
of  designing  a  rectangular  footing.  First,  the  area  must  be 
found;  then  it  must  be  properly  located;  and,  finally,  it 
must  be  properly  strengthened  to  resist  the  incurred  bending 
moment. 

However,  owing  to  the  shape  of  the  footing,  the  formulas 
are  more  complicated  than  the  ones  given  for  rectangular 
footings.  To  illustrate  their  use,  reference  is  made  to  Fig.  22, 
which  shows  a  plan  view  and  a  conventional  side  view  of  a 
fan-shaped  footing.  In  the  side  view,  the  loads  and  reactions 
are  represented  by  the  shaded  areas. 

Let  Q  be  the  pressure  per  square  inch  on  the  soil.  Then, 
niQ  =  Pl  is  the  pressure  per  linear  inch  at  one  end  of  the 
footing,  and  n2Q  =  P2  is  the  pressure  per  linear  inch  at  the 
other  end  of  the  footing.  The  letters  used  in  the  formulas 
are  shown  in  the  illustration  and  will  be  readily  understood. 

The  formulas  for  the  points  of  no  shear  are: 


P1-P2I 


Pi  ~  wi  + 


i\-P.X 


Pi- 


2(P,-pjiy, 

1 


1 

P  —P 

1  1  L  2 


X 


Pl-w2  + 


\2(Pt-Pt) 


[w2  (yt  +  xt  +  y2)  -  IUJ  +  (w2  -  Pt): 


(3) 


After  the  values  of  llt  l2,  and  l3  have  been  found,  the  bending 
moment  at  these  three  places  must  be  obtained  by  the  follow¬ 
ing  formulas: 


M,  =  -  (ij_  P2)/L  _  (/  -y  y. 

2  0/  2 


40 


HEAVY  FOUNDATIONS 


§38 


m2=^1- — qf---  ^-y.-f)  (5) 

M  3  =  l±ll-{Z±zIM--W  \(l,  3-y  ,-^i) 

2  61  \  2/ 

-^Ik-fo+xi+yJ?  (6) 


26.  The  design  of  a  footing  and  the  use  of  these  formulas 
is  best  illustrated  by  the  following  example:  Design  a  fan¬ 
shaped  footing  to  support  two  columns.  One  carries  350  tons, 
and  the  other  85  tons.  The  two  columns  are  12  feet  apart. 
The  soil  will  safely  carry  5  tons  per  square  foot. 

First,  the  area  must  be  determined.  The  total  load  is 
350  +  85  =  435  tons.  The  required  area  of  the  footing  is 
therefore  435  =  5  =  87  square  feet.  In  actual  practice,  the 
designer  usually  tries  different  sizes  of  footings  until  he 
strikes  one  of  the  right  area,  or  he  may  assume  all  the. dimen¬ 
sions  but  one  and  solve  for  that  one,  as  follows:  Assume 
that  the  width  of  the  small  end  of  the  footing  is,  say,  1  foot 
6  inches  and  that  the  length  of  the  footing  is  18  feet  10  inches. 
It  remains  to  find  out  what  the  length  of  the  wide  end  will  be. 
Call  this  x.  Then,  by  the  rules  of  geometry,  the  area  of  the 

footing  is  %Jr  1:-5X  18  =  87;  and  %  =  8.1667  feet,  or  8  feet 


2  inches. 

The  next  point  is  to  locate  the  center  of  gravity  correctly. 
First,  the  center  of  gravity  of  the  two  loads  must  be  obtained. 
To  find  this,  take  moments  about  the  larger  load.  The 
work  is  as  follows: 


Load 

Moment  Arm 

Moment 

350 

0 

0 

85 

12 

1,020 

Total,  435 

1,020 

The  distance  of  the  center  of  gravity  from  the  larger  load 
is  therefore  1,020  =  435  =  2.34  feet. 


HEAVY  FOUNDATIONS 


41 


§  3S 


Next,  lay  out  the  area  of  the  footing,  as  shown  in  Fig.  23. 
To  find  its  center  of  gravity,  take  moments  about  the  line  a  b. 
For  convenience,  the  area  abed  is  divided  into  two  parts, 
a  triangle  and  a  parallelogram,  by  the  line  d  e  parallel  to  c  b. 
Its  center  of  gravity  is  then  found  as  follows: 


Moment 

Value  Arm  Moment 

Area  ade . 6.667X9  =  60  6  360 

Area  e  b  c  d .  1.5X18  =  27  9  243 

Total .  87  603 


The  moment  divided  by  the  total  area  is  603-^87,  or 
6.93  feet.  Therefore,  the  center  of  gravity  of  the  area  is 
6.93  feet  to  the  right  of  a  b,  and  this  same  place  must  be 
2.34  feet  to  the  right  of  the  left-hand  column.  The  columns 


may  now  be  located  on  the  diagram,  Fig.  23,  as  shown.  It 
is  assumed  that  the  base  of  the  heavier  column  is  2  feet  on 
a  side  and  that  the  base  of  the  lighter  column  is  18  inches 
square. 

The  last  consideration  is  to  find  the  maximum  bending 
moment  and  then  proportion  the  beams  to  resist  this  moment. 


The  pressure  on  the  soil  is  5  tons  per  square  foot,  or 


5X2,000 

144 


=  69.44  pounds  per  square  inch.  From  the  figure,  Wj  =  98 
and  w2=18.  Therefore,  =  69.44  X  98  =  6,805.12  pounds 

and  P2  =  69.44 X  18=  1,249.92  pounds.  Wx  =  700,000  pounds: 


42 


HEAVY  FOUNDATIONS 


§38 


W2=  170,000  pounds;  wt  =  700,000-^24  =  29,167  pounds;  w2 
=  170,000  -T- 18  =  9,444  pounds;  ^  =  43.08  inches;  ^  =  24 

P  —P 

inches,  y2  =  123  inches;  /=  12X18  =  216;  and  — - - - 

1 

6,805.12-1,249.92  0K_0_  ,  ™  Px-P* 

=  — - — - - ——  =  25.7185  pounds.  Whenever  — - 

216  l 

occurs  in  the  formulas,  the  value  just  found  may  be  used;  it  is 
also  evident  that  the  reciprocal  of  this  value  may  be  used  for 

l 


P  !  P  2 

Substituting  in  formulas  1,  2.  and  3,  Art.  25, 

1 


k  = 


X  [6,805.12-29,167 


25.7185 

+  V2  X  43.08  X  29,167  X  25.7185  +  (29,167  -  6,805. 12)2] 

=  54.48  inches 


X  (6,805.12-  V(3,805. 122 - 2 X 25.7185 X 700, OOO) 


25.7185 


=  139.79  inches 


L  = - - —  X  [6805. 12  -  9,444  +  a/2  X  25.7185[9,444 

25.7185 

X  (43.08  +  24  +  123)  -  700,000]  +  (9,444  -  6,805. 12)2] 

=  206.73  inches 

Now  that  the  values  of  lv  l2,  and  l3  have  been  found,  the 
bending  moments  may  be  found  by  formulas  4,  5,  and  6, 
Art.  25.  Substituting  the  correct  values  in  these  formulas, 


6,805. 12  X  54. 482  25.7185  X  54.483  29, 167 


2  6  2 

X  (54.48 -43.08)2  =  7,510,650.345  inch-pounds 

M  =  6,805.12X  139.792  _  25.7185X139.793  _ 

2  2  6 

X  (139.79- 43.08 -V)=  -4,515,822.49  inch-pounds 


§38 


HEAVY  FOUNDATIONS 


43 


M  =  6,805. 12 X2Q6.732 _  25.7185 X  206.733 _  7QQ  Q()0 


X  (206.73-43.08— V) 


9,444 


6 


X [206.73 -  (43.08  +  24  + 123)  f 


=  81,322.12  inch-pounds 


From  the  foregoing,  it  can  be  seen  that  the  greatest  bending 
moment  occurs  at  lt  and  is  7,510,650.35  inch-pounds.  Let  it 
be  assumed  that  only  four  beams  are  used  in  this  grillage. 
Each  beam  must  therefore  resist  7,510,650.35-^4  or  approxi¬ 
mately  1,877,663  inch-pounds.  If  the  allowable  stress  is 
18,000  pounds,  the  required  section  modulus  will  be  1,877,663 
-T- 18,000=  104.3.  By  referring  to  Table  II,  it  will  be  seen  that 
a  20-inch  65-pound  beam  will  fill  the  requirements. 

The  arrangement  of  the  beams  at  the  small  end  of  the 
footing  is  shown  in  Fig.  24.  It  will  be  noticed  that  two  of 


them  are  ended  short  of  the  column  carrying  the  lighter 
load,  but  this  grillage  is  sufficiently  strong,  as  the  bending 
moment  at  the  small  end  of  the  footing  is  not  great.  The 
beams,  it  will  be  noticed,  are  placed  only  2  inches  apart 
instead  of  3,  the  .usual  distance.  This  is  done  to  save  room. 

The  design  of  the  short  cross-beams  directly  under  each 
column  may  now  be  considered.  The  beams  under  the 
heavier  loaded  column  will  be  considered  first.  The  bending 
moment  may  be  determined  by  the  formula  of  Art.  9.  Here, 
w  =  700,000  pounds;  x  =  24  inches;  and  /  =  / g,  Fig.  23.  The 


44 


HEAVY  FOUNDATIONS 


§  38 

value  of  /  g  may  be  found  by  scale  or  by  calculation,  and  is 
equal  to  82.04,  say  82,  inches. 

Substituting  these  values  in  the  formula, 

.  M  =  ^5--  x  (82  -  24)  =  5,075,000  inch-pounds 

8 

If  four  beams  are  used,  each  one  would  have  to  resist 
5,075,000 -r- 4=  1,268,750  inch-pounds.  If  the  allowable  unit 
stress  is  18,000  pounds,  the  required  section  modulus  will  be 
1,268,750-^-18,000  =  70.5,  almost.  By  referring  to  Table  II, 
it  will  be  seen  that  an  18-inch  55-pound  beam  will  answer 
the  purpose. 

On  account  of  the  very  small  overhang  of  the  beams  under 
the  base  of  the  column  supporting  the  smaller  load,  it  will 
not  be  necessary  to  figure  the  size  of  the  cross-beams;  as  a 
matter  of  fact,  they  may  be  omitted  entirely  if  so  desired. 


CANTILEVER  FOUNDATIONS 


DETAIIjS  of  construction 

27.  In  crowded  sections  of  large  cities  the  building  sites 
have  great  value;  therefore,  in  order  to  obtain  adequate 
remuneration  on  an  investment  it  is  necessary  to  utilize 
every  foot  of  building  area.  It  is  sometimes  possible  to 
get  good  rental  from  basements  and  subbasements,  so  that 
it  is  quite  common  for  an  important  building  to  have  three 
or  four  floors  below  the  ground  level,  these  basement  floors 
being  supplied  with  artificial  light  and  ventilation.  Such 
unusual  conditions  require  special  features  of  construc¬ 
tion,  and  it  is  therefore  not  uncommon  in  the  erection  of 
high  buildings  to  employ  what  are  known  as  cantilever 
foundations. 

28.  In  Fig.  25,  the  foundation  of  an  old  building  that 
has  a  building  of  skeleton  construction  adjacent  to  it  is 
shown  at  a.  It  is  evident  that  to  build  close  against  the 


HEAVY  FOUNDATIONS 


45 


Fig.  26 

iron  base  of  the  wall  column  is  carried  on  a  concrete  footing 
course  a,  and  the  entire  weight  of  the  outside  wall  of  the 


building  line  yy  and  to  get  adequate  foundation  area  for 
the  support  of  the  column  b,  all  the  batter  of  the  footing 
must  be  inside  the  building.  In 
constructing  the  footings  in  this 
manner,  the  center  of  downward 
pressure  from  the  column  does  not 
coincide  with  the  center  of  upward 
pressure  from  the  soil,  and  the 
condition  shown  by  the  arrows  c 
and  d  exists.  Therefore,  it  is  evi¬ 
dent  that  some  special  means  must 
be  provided  to  centralize  over  the 
foundations  the  concentrated  loads 
from  the  outside  columns,  and  at 
the  same  time  utilize  every  inch 
of  ground  surface  by  building  close 
to  the  line.  This  condition  is  met 
by  adopting  the  construction  shown 
in  Fig.  26.  In  this  case,  the  cast-  Fig.  25 


46 


HEAVY  FOUNDATIONS 


§38 


new  building  adjacent  to  the  existing  wall  at  b  is  carried  by 
the  overhang  of  the  girder  at  c.  By  this  means  the  new  wall 
is  carried  close  to  the  old  wall,  and  the  center  of  weight 
from  the  combined  loads  above  and  the  center  of  pressure 
from  beneath  on  the  combined  footings  coincide. 

By  inspecting  Fig.  26,  it  will  be  evident  that  the  girder  d 
is  subjected  to  great  bending  stress  at  or  adjacent  to  the 
point  e,  and  that  also,  if  the  wall  and  the  loads  supported  by 


Fig.  27 


the  outside  column  /  are  great,  there  will  be  an  upward 
lifting  tendency,  as  shown  by  the  arrow  g.  Therefore,  the 
conditions  of  loading  must  be  investigated  to  determine 
whether  the  weight  on  the  column  h  multiplied  by  the  lever 
arm  x  is  equal  to  or  greater  than  the  weight  on  the  column  / 
multiplied  by  the  lever  arm  xv  Frequently,  the  overhang  is  so 
great  and  the  dead  loads  on  the  interior  column  h  are  so  small 
that  it  is  necessary  to  anchor  securely  the  column  h  to  a 
heavy  foundation  that  supplies  the  necessary  weight  so  as  to 


§38 


HEAVY  FOUNDATIONS 


47 


overcome  any  tendency  of  the  load  on  the  overhang  to  lift 
the  interior  column. 

29.  Another  condition  that  sometimes  requires  the  adop¬ 
tion  of  the  cantilever  foundation  is  shown  in  Fig.  27.  In 
order  to  obtain  the  headroom  for  the  subbasement,  it  is  neces¬ 
sary  to  excavate  below  the  foundation  of  an  old  building 
adjacent  to  it.  Such  excavation  would  require  either  that  the 
old  building  be  underpinned  and  a  new  foundation  carried 
down,  together  with  the  foundation  of  the  new’  building, 
as  designated  by  the  dotted  lines,  or  that  the  foundation 
footings  for  the  new  building  be  located  farther  within  the 
site.  In  order  to  accomplish  the  latter,  cantilever  construc¬ 
tion  could  be  adopted,  as  shown.  When  such  construction 
is  employed,  the  excavation  for  the  footings  a  can  be  made 
without  disturbing  the  footings  beneath  the  old  building, 
though  such  footings  must  not  encroach  on  the  natural 
slope  of  the  soil  on  which  the  old  footings  are  built. 

30.  In  Fig.  28  is  illustrated  a  type  of  cantilever  founda¬ 
tion  used  in  a  large  office  building.  This  foundation  con¬ 
struction  was  used  in  order  to  bring  the  column  loads  over 
the  center  of  gravity  of  the  combined  footings  and  to  prevent 
the  footings  from  overrunning  the  property  line.  Columns 

a,  b,  c,  and  d  are  carried  on  cantilever  girders  e ,  which  in 
turn  are  supported  by  cantilever  girders  /.  These  girders  in 
turn  are  supported  on  distributing  girders  resting  on  a  raft  or 
grillage  footing  g.  In  this  way  the  grillage  footing  is  prac¬ 
tically  symmetrically  loaded  and  will  produce  an  approx¬ 
imately  uniform  bearing  stress  on  the  soil,  which  will  insure 
its  uniform  settlement. 

In  Fig.  29  are  shown  several  details  of  a  cantilever  grillage 
footing  very  similar  to  that  shown  in  Fig.  28.  Over  and 
under  each  set  of  girders  where  there  is  a  concentrated 
load,  each  girder  is  well  stiffened  by  vertical  stiffeners  a, 

b ,  and  c.  These  stiffeners  are  ground  to  fit  between  the 
flange  angles  of  the  girders.  The  girders  d  are  retained 
against  any  tilting  tendency  that  might  exist  by  the  gusset- 
plate  brace  e. 


•Secf/ono/  £/erafion  X.-X 


Mam  WaJ/  Footing 


L/evaf/on  on  Z-Z 


i _ i~::::::::. 


Fig.  28 


48 


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O'  O  OOP 


Lower 

CanWerer 

G/re/ers 


o  o  o  o  o 
Q  o  o  o'  o  o 


a 


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o 

o  o 

o  o  o 

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ll 

Ends  of  a//  t/ertica/  IVefi  Stiffener 
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§38 


/8~/{ - »r*  - /5-/o£ 


X 

XI 

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s7z/- 


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le-,//- 


H  / 


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J+r/Z' 


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H 

£ 


211—28 


'ng/tud mal  Sect/on. 


50 


HEAVY  FOUNDATIONS 


§38 

31.  Another  type  of  cantilever  foundation  construction 
is  shown  in  Fig.  30.  In  this  case,  three  column  footings  are 
supported  on  a  grillage,  the  two  outside  columns  forming 
the  support  for  a  cantilever  box  girder  that  sustains  the 
outside  wall  of  the  building.  The  plan  of  the  foundation  is 
shown  in  view  (a)  and  the  elevation  in  ( b ).  The  outside 
distributing  girder  sustaining  the  column  that  supports  the 
cantilever  is  of  heavy  box-girder  construction,  while  the 
distributing  girders  under  the  interior  columns  are  20-inch 
85-pound  I  beams.  The  detail  of  the  cantilever  girder  is 
shown  in  Fig.  31,  and  on  examination  should  be  sufficiently 
clear  as  to  details  of  construction  without  further  explanation. 


DESIGN  OF  CANTILEVER  FOUNDATIONS 

32.  The  design  of  a  cantilever  foundation  divides  itself 
into  two  parts:  (1)  The  design  of  the  girder  to  resist  the 
bending  moments,  and  (2)  the  design  of  the  footings  them¬ 
selves. 

It  is  not  within  the  province  of  this  Section  to  discuss  the 
design  of  the  steel  girders  used  as  cantilevers,  while  the 
method  of  designing  reinforced-concrete  girders  to  resist 
the  moment  incurred  is  given  in  another  Section.  The 
maximum  moment  is  usually  found  to  be  at  the  center  line 
of  the  outside  footing,  as  at  e,  Fig.  26.  The  moment  is  the 
load  on  the  outside  column  multiplied  by  the  horizontal 
distance  between  the  center  line  of  the  outside  column 
and  the  center  line  of  the  outside  footing;  that  is,  in  Fig.  26, 
it  is  the  load  at  /  times  the  distance  and  the  girder,  whether 
of  steel  or  of  concrete,  must  be  designed  to  withstand  this 
moment. 

The  greatest  care  must  be  exercised  both  in  the  selection 
of  the  material  and  in  the  inspection  of  the  workmanship 
of  these  important  structural  members,  for  their  failure 
will  ordinarily  mean  the  destruction  of  the  entire  building. 
Owing  to  the  fact  that  steelwork  of  the  cantilever  construction 
is  in  a  location  where  more  than  ordinary  corrosion  may 


§38 


HEAVY  FOUNDATIONS 


51 


take  place  with  little  possibility  of  its  discovery  or  prevention, 
the  steelwork  should  be  designed  with  a  high  factor  of  safety. 
Such  a  procedure  is  at  all  times  a  wise  precaution  and  will 
allow  for  considerable  deterioration  without  dangerously 
affecting  the  safe  strength  of  the  foundation. 

33.  The  footing  area  must  be  designed  by  the  same 
method  as  used  before;  that  is,  the  common  center  of  gravity 
of  the  footing  areas  must  coincide  with  the  common  center 
of  gravity  of  all  the  loads.  The  beams  in  each  individual 
footing  are  of  course  designed  to  support  the  load  on  that 
footing  by  the  methods  previously  given  in  this  Section. 

Referring  to  Fig.  26  and  its  description,  it  was  suggested 
that  occasionally  the  load  on  /  multiplied  by  xl  would  be  greater 
than  the  load  on  h  multiplied  by  x.  In  such  a  case,  the 
column  h  would  tend  to  rise,  and  it  would  be  restrained  only 
by  the  rigidity  of  the  building  and  the  weight  of  the  founda¬ 
tion  under  it,  to  which  it  is  anchored.  Under  such  circum¬ 
stances,  it  is  evident  that  the  unit  pressure  on  the  foundation  a 
would  be  greater  than  that  on  the  foundation  under  h, 
because  the  foundation  a  takes  the  load  from  f  and  h,  while 
the  foundation  under  h  only  supports  part  of  its  own  weight 
and  yet  has  to  be  made  of  considerable  size  to  insure  that  the 
column  h,  which  is  anchored  to  it,  will  not  rise.  Therefore, 
under  the  assumed  conditions,  the  footing  a  will  settle  more 
than  the  footing  under  h,  as  the  latter  will  hardly  sink 
at  all. 

If,  as  is  usually  the  case,  the  location  of  the  columns  is 
fixed  by  circumstances,  there  are  but  two  ways  of  overcoming 
this  difficulty.  The  first  method  is  either  to  sink  the  founda¬ 
tion  a  to  solid  rock  or  to  put  piles  under  it,  so  that  it  will 
not  settle  no  matter  what  load  is  put  on  it.  The  second 
method  is  to  extend  the  girder  of  the  footing  to  include 
three  columns.  Such  an  arrangement,  in  which  the  footing 
is  extended,  is  shown  in  Fig.  30,  and  another  example,  in 
which  the  girder  is  extended,  is  shown  in  Fig.  32.  However, 
such  measures  seldom  have  to  be  taken,  as  most  cantilever 
foundations  have  two  footings  and  a  load  on  each  one. 


<N 

CO 

6 

fa 


52 


HEAVY  FOUNDATIONS 


53 


§ 


38 


34.  As  already  explained,  the  principle  used  in  propor¬ 
tioning  the  footings  for  a  cantilever  foundation  does  not  differ 
from  the  one  employed  for  any  other  foundation.  The 
following  example  will  make  the  method  of  procedure  plain: 
In  Fig.  33  is  shown  the  center  line  of  two  columns  located 
18  feet  apart.  The  inside  one  carries  200  tons,  and  the  out¬ 
side  one  300  tons.  Owing  to  the  interference  of  the  founda¬ 
tions  of  the  adjoining  building,  the  edge  of  the  outside  footing 
cannot  approach  the  center  line  of  the  outside  column  any 
nearer  than  2  feet.  The  soil  will  carry  5  tons  per  square 
foot.  Design  the  footing. 

First,  the  total  area  of  the  footing  must  be  obtained.  The 
total  load  is  200  +  300  =  500  tons.  Therefore,  the  total  area 
is  500-^5=  100  square  feet.  Next,  the  location  of  the  outside 


-/8-0-- 


- -  3-0 

fe} 

1 

tal 

1 

I 

I 


Fig.  33 


footing  may  be  determined.  Its  edge  is  located  by  the  con¬ 
dition  of  the  problem  at  2  feet  from  the  center  line  of  the 
column.  Its  center  line,  which  is  the  governing  feature, 
may  arbitrarily  be  located  5  feet  from  the  center  line  of  the 
column.  This  would  allow  a  footing  6  feet  wide  without 
encroaching  on  the  2  feet  next  to  the  column.  The  next 
step  is  to  find  the  location  of  the  line  of  action  of  the  center 
of  gravity  of  the  two  column  loads.  To  do  this,  take  moments 
about  the  center  line  of  the  inside  column  as  follows: 


Load 

Tons 

Moment 

Arm 

Moment 

Inside  column . 

. . . 200 

0 

0 

Outside  column . . . 

. .  . . 300 

18 

5,400 

T  otal . 

. . . 500 

5,400 

54 


HEAVY  FOUNDATIONS 


§38 


The  distance  of  the  center  of  gravity  of  the  loads  from  the 
center  line  of  the  inside  column  is  therefore  5,400 -f- 500 
=  10.8  feet.  The  footing  under  the  inside  column  can,  as 
usual,  be  directly  centered  under  the  column.  Call  the  area 
of  this  footing  x,  and  the  area  of  the  outside  footing  y. 
Then  x  +  y=100  square  feet.  The  distance  from  the  common 
center  of  gravity  of  both  footings  to  the  center  line  of  the 
inside  column  is  found  as  follows: 

Area  Moment  Arm  Moment 


y 


o 

18-5=13 


0 

13  y 
13  y 


Total,  x  +  y 

The  distance  of  the  common  center  of  gravity  of  the  two 
footings  from  the  center  line  of  the  inside  column  is  there¬ 
fore  ^  ^  This  distance,  if  the  pressure  on  the  footings 

x  +  y  100 

1 3  y 

is  to  be  uniform,  must  equal  10.8.  Therefore, — -  =10.8,  or 

100 


y  =  83.08,  approximately,  and  x}  or  the  area  of  the  other 
footing,  will  equal  100  —  83.08=16.92  square  feet.  Assume 
that  the  outside  footing  is  of  its  maximum  width,  namely, 
6  feet.  Then  its  length,  which  will  run  at  right  angles  to  the 
length  of  the  girder  on  which  the  columns  rest,  will  be  83.08 
4-6=13.85  feet,  say  13  feet  10  inches.  Assume  that  the 
footing  under  the  inside  column  is  square.  Its  area  is  16.92 
feet.  Therefore,  its  length  on  a  side  will  be  4.11  feet,  say 
4  feet  1  inch. 

All  dimensions  of  footings  to  be  used  under  cantilever 
girders  may  be  obtained  by  the  method  just  outlined. 


EXAMPLES  FOR  PRACTICE 

1.  A  cantilever  foundation  supports  two  columns  located  20  feet 
apart.  Each  column  carries  300  tons.  The  soil  will  carry  safely  6  tons 
per  square  foot.  One  footing  is  directly  under  the  inside  column, 
and  the  other  has  its  center  line  4  feet  from  the  center  line  of  the 
outside  column.  Find  the  area  of  each  footing. 

a  ,  f  Inside  footing,  37.5  sq.  ft. 
ns.  j  Outside  footing,  62.5 sq.  ft. 


§38 


HEAVY  FOUNDATIONS 


55 


2.  A  cantilever  foundation  supports  two  columns  placed  12  feet 
apart.  The  outside  column  carries  100  tons,  and  the  inside  one 
carries  60  tons.  The  inside  footing  is  directly  under  the  inside 
column,  and  the  center  line  of  the  outside  footing  is  2  feet  inside  the 
center  line  of  the  outside  column.  The  safe  bearing  value  of  the  soil 
is  7  tons  per  square  foot.  Find  the  area  of  each  footing. 

A  /Inside  footing,  5.72  sq.  ft. 
ns'  [Outside  footing,  17.14  sq.  ft. 


%i  . 


‘ 

. 


WOOD  AND  METAL  PILES 


VARIETIES  OF  PILES 


INTRODUCTION 

1.  Definition. — A  pile  may  be  considered  as  a  column 
with  a  base  more  or  less  rigid,  according  to  the  nature  of  the 
soil  into  which  it  is  driven.  If  a  stick  is  driven  into  yielding 
soil,  it  will  stand  upright  and  support  a  load,  even  though 
it  may  not  have  reached  a  firm  bottom,  the  friction  of  the 
soil — or  the  pressure  of  its  particles  against  the  sides  of  the 
stick  or  pile — holding  it  in  place.  Thus,  when  a  pile  is  driven 
into  the  ground  and  it  does  not  reach  solid  rock,  it  is  pre¬ 
vented  from  entering  further  into  the  soil  by  the  friction 
against  its  sides. 

2.  Classification  of  Piles. — Whatever  may  be  their 
form  or  material,  piles  are  often  classified  with  reference  to 
the  special  purpose  they  are  intended  to  serve. 

Bearing  piles  are  those  used  to  support  vertical  forces 
or  loads;  to  this  class  belong  the  great  majority  of  piles  used 
in  engineering  construction. 

Protection  piles  are  piles  driven  singly  or  in  groups  or 
rows  to  protect,  or  shield,  a  structure  from  external  injury. 

Anchor  piles,  or  mooring  piles,  are  used  singly  or  in 
groups  for  holding  or  anchoring  vessels  and  other  floating 
structures. 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS1  HALL,  LONDON 

§  39 


2 


PILING 


§39 

Both  protection  and  anchor  piles  are  usually  of  the  same 
design  as  bearing  piles. 

3.  Terms  Used  in  Piling;. — The  technical  terms 
used  in  pile  driving  are  descriptive  of  the  form  or  position 
of  the  piles,  or  the  manner  of  their  driving. 

A  close  pile  is  one  set  close  to  another  when  the  pile 
already  driven  shows  signs  of  weakness. 

A  follower  is  a  short  pile  or  timber  set  on  top  of  a 
pile,  the  head  of  which  is  to  be  driven  below  the  surface  of 
the  water.  The  follower  is  often  used  when  the  head  of  the 
pile  reaches  the  surface  of  the  water,  the  driving  being  con¬ 
tinued  until  the  first  pile  reaches  the  proper  depth. 

A  test  pile  is  one  driven  to  test  the  nature  of  the  soil 
and  its  resistance  to  pile  driving. 

A  gauge?  or  guide,  pile  is  any  one  of  a  number  of  piles 
driven  to  outline  the  desired  course. 

A  filling  pile  is  any  one  of  several  piles  placed 
between  the  gauge  piles. 


WOODEN  BEARING  PIEES 

4.  Wooden  bearing  piles  are  generally  round,  and 
from  12  to  20  inches  in  diameter  at  the  head  and  at  least 
5  inches  in  diameter  at  the  small  end.  They  should  be 
straight  and  free  from  bark  and  projecting  limbs,  but  if  they 
are  to  be  exposed  to  the  rise  and  fall  of  tides,  it  is  considered 
best  to  drive  them  with  the  bark  on,  because  they  are  then 
not  so  liable  to  be  attacked  by  marine  wood  borers.  There 
are  five  marine  creatures  that  do  most  of  the  destructive 
work  to  piles.  Two  of  them,  the  Xylotrya  and  the  Teredo , 
look  something  like  worms,  and  the  other  three,  known  as 
the  Limnoria,  the  Chelura,  and  the  Sphceroma,  resemble 
insects. 

The  principal  timbers  used  in  piling  are  long-leaf,  short- 
leaf,  and  loblolly  pine,  white  and  red  oak,  Douglass  fir,  spruce, 
redwood,  cedar,  cypress,  eucalyptus,  and  palmetto.  Of  these, 
the  first  six  have  the  widest  use,  the  pines  and  oaks  on  the 


§39 


PILING 


3 


Atlantic  Coast  and  the  coast  of  the  Gulf  of  Mexico,  and  the 
fir  on  the  Pacific  Coast.  The  others  are  used  only  locally. 
Oak  has  the  advantage  of  being  hard  and  tough,  and  stands 
hammering  well,  but  it  cannot  be  obtained  in  as  large,  straight, 
or  long  pieces  as  spruce,  hard  pine,  or  cypress.  The  long- 
leaf  pine  is  hard  and  tough  and  can  be  readily  obtained  in 
good-sized  logs  of  lengths  up  to  90  or  100  feet,  and  from 
12  to  18  inches  diameter  at  the  butt  and  from  5  to  12  inches 
thick  at  the  lower  end. 


5.  Piles  are  usually  driven  with  their  small  ends  down. 
The  butt  end  is  cut  off  square,  to  receive  the  hammer  squarely. 
The  small  end  is  usually  pointed  to  an  angle  of  about  30°  and 


Fig.  1 


is  often  shod  with  iron.  If  the  pile  is  to  be  used  in  very  soft 
soil,  it  is  often  better  to  leave  the  small  end  blunt,  because, 
when  the  pile  has  but  little  lateral  support,  any  small  obstruc¬ 
tion  is  liable  to  deflect  the  pointed  end,  while  a  blunt  pile 
will  drive  such  small  obstacles  before  it. 

6.  The  large  end  of  the  pile  should  be  cut,  or  chamfered, 
for  a  few  inches  from  the  end,  so  that  a  wrought-iron  ring 
1  inch  in  thickness  and  3  inches  wide  will  fit  over  the  end 
of  the  pile  tightly,  as  shown  in  Fig.  1  (a),  when  struck  one  or 
two  light  taps  with  a  hammer  or  ram.  Sometimes  a  ring 
from  1  to  U  inches  smaller  in  diameter  than  the  pile  is  simply 
placed  on  the  top  of  the  pile  and  then  driven  into  it  with 
light  blows.  This  method,  however,  is  not  so  desirable  as 


4 


PILING 


§39 


the  former,  as  the  ring  is  liable  to  split  long  pieces  from  the 
sides  of  the  piles,  and,  not  usually  being  put  on  until  the  pile 
is  more  or  less  battered  on  the  end,  is  likely  to  be  carelessly 
placed,  and  not  concentric  with  the  head  of  the  pile.  The 
rings  are  used  in  pile  driving  in  order  to  lessen  the  tendency 
of  the  pile  to  split  or  broom.  Brooming  is  a  term  applied  to 
the  splintering  of  the  fibers  on  the  end  of  the  piles,  due  to 
repeated  blows  of  the  ram. 

7.  Shoeing;  of  Piles. — In  driving  piles  through  soft 
material  to  rock  or  hard  gravel,  the  force  of  the  blows  of  the 
hammer  has  a  tendency  to  split  the  lower  end  of  the  piles 
after  rock  or  hard  gravel  has  been  reached,  thus  greatly 
impairing  their  bearing  capacity.  To  prevent  this,  piles  are 
often  protected  at  the  end  with  wrought-  or  cast-iron  shoes. 

Fig.  1  illustrates  three  methods  of  shoeing  the 
ends  of  piles.  In  ( b )  is  shown  a  2"  X  wrought- 
iron  strap  a  bolted  through  the  pile  b,  forming  a 
shoe,  which  is  the  same  on  both  sides  of  the  pile. 
In  (c)  is  shown  a  cast-iron  conical  shoe  fitted  over 
the  end  of  the  pile  b.  The  head  of  the  shoe  c 
protects  the  end  of  the  pile,  and  the  straps  a,  one 
on  each  side,  hold  the  shoe  in  place.  One  of  the 
best  forms  of  cast-iron  shoes  is  shown  in  (d).  In 
this  case,  the  pile  has  a  blunt  end  from  4  to  6  inches 
in  diameter,  shown  at  b.  The  shoe  has  a  solid  conical  point  c, 
the  top  of  its  base  being  about  the  same  diameter  as  the  end 
of  the  pile;  the  straps  a  then  extend  upwards  on  the  sides  of 
the  pile  and  are  bolted  or  spiked  to  it,  as  shown.  The  straps 
and  bolts  hold  the  shoe  in  place  while  it  is  pushed  through 
the  soil. 

8.  Splicing  of  Piles. — When  a  firm  subsoil  cannot 
be  obtained  except  at  a  very  great  depth  below  the  surface, 
so  that  it  becomes  impracticable,  if  not  impossible,  to  obtain 
timber  piles  of  the  requisite  length,  the  piles  may  have  to  be 
spliced.  In  general,  a  splice  is  some  form  of  joint  con¬ 
necting  the  ends  of  two  piles.  It  may  be  a  dowel,  or  iron  bar, 
about  2  feet  long,  embedded  about  1  foot  in  the  end  of  each 


§39 


PILING 


5 


pile,  as  illustrated  in  Fig.  2,  or,  if  both  piles  have  the  same 
diameter  at  the  splice,  the  method  shown  in  Fig.  3  may  be 
used.  Here,  the  first  pile  is  shown  at  a;  the  follower,  at  b, 
and  a  dowel  to  preserve  the  alinement  of  the  two  piles,  at  c. 
At  d  are  shown  wrought-iron  straps,  made  usually  of  2"Xi" 
X20"  iron,  to  bind  the  two  piles  together. 

9.  A  still  more  secure  joint  consists  of  a  band 
of  iron,  at  least  12  inches  long  and  of  as  great  a 
diameter  as  necessary,  to  which  the  ends  of  both 
piles  are  fitted.  To  prevent  the  band  from  being 
jarred  either  up  or  down,  away  from  the  joint, 
spikes  are  driven  into  the  piles  immediately  above 
and  below  the  band,  as  illustrated  in  Fig.  4. 

10.  When  the  ground  is  in  a  partly  fluid 
state,  it  may  have  so  little  stiffness  that  the 


Fig.  3 


Fig.  4 


Fig.  5 


jointed  pile  is  likely  to  buckle  at  the  joint,  unless  the  splice 
is  made  in  the  form  of  scarfs ,  which  consist  of  six  or  eight 
timbers,  about  3  inches  square  in  sectional  area  and  8  to  10 
feet  long,  spiked  to  the  piles,  as  shown  in  Fig.  5. 

Whatever  form  of  splice  is  used,  the  first,  or  lower,  pile  is 
driven  into  the  ground  until  its  top  is  but  a  few  feet  above 
the  surface;  then  the  second  pile  is  spliced  on  and  driven  in. 
Of  course,  the  force  required  for  driving  in  a  soil  so  soft  that 
very  long  piles  are  necessary  is  correspondingly  small. 


6 


Fig. 


§39 


PILING 


7 


1  i.  Protection  of  Piles. — When  timber  foundations 
have  to  be  constructed,  and  the  piles  are  exposed  to  sea-water, 
they  are  liable  to  be  attacked  by  various  wood-boring  worms, 
as  previously  stated.  These  will  penetrate  the  piles  and 
destroy  ordinary  timber  in  from  3  to  5  years.  Fig.  6  shows 
a  section  broken  off  a  pile  that  has  been  attacked  by  wood¬ 
boring  worms.  It  can  readily  be  seen  that  the  wood  is  so 
honeycombed  that  its  entire  strength  may  be  said  to  be  lost. 
To  protect  the  pile  against  wood  borers,  the  bark,  as  pre¬ 
viously  mentioned,  is  often  left  on,  for  they  do  not  bore 
through  the  bark  of  piles. 


Fig.  7 


To  prevent  the  attack  of  these  destroyers,  piles  are  often 
treated  with  creosote,  or  the  heavy  oil  of  tar.  The  sap  and 
moisture  are  exhausted  from  the  wood  by  creating  a  partial 
vacuum  in  an  air-tight  vessel  or  tank  into  which  the  piles 
have  been  placed,  and  then  the  creosote  is  forced  into  the 
pores  of  the  timber  under  heavy  pressure.  By  this  means, 
the  depredations  of  the  wood  borers  are  almost  completely 
checked.  Wooden  piles  are  also  frequently  charred  slightly 
on  the  outside,  to  allow  the  creosote  to  penetrate  more 
readily. 


8 


PILING 


§39 


Another  method  of  protecting  piles  from  these  creatures 
is  to  bore  a  hole  in  the  center  of  the  pile  and  then  force 
corrosive  sublimate  into  it.  The  hole  is  then  plugged  to  keep 
the  salt  in. 

12.  Wooden  piles  that  are  placed  in  sea- water  are  some¬ 
times  covered  with  some  material  that  the  wood  borers  cannot 
penetrate.  These  materials  include  concrete,  either  solid  or 
in  the  form  of  a  pipe,  terra-cotta  pipe,  etc. 

Fig.  7  shows  a  pier  erected  on  wooden  piles  driven  in 
clusters  of  four.  Each  cluster  is  embedded  in  concrete 
reinforced  with  expanded  metal.  To  hold  the  concrete  in 

place  while  it  is  setting  and  to  protect 
it  from  abrasion  afterwards,  the  entire 
shaft  is  covered  with  wooden  staves 
that  are  held  together  by  means  of  steel 
hoops.  This  form  of  pile  is  really  half 
way  between  a  timber  pile  and  a  con¬ 
crete  pile.  The  concrete  protects  the 
timbers  efficiently  from  the  marine  wood 
borers. 

13.  In  covering  piles  with  ordinary 
terra-cotta  pipe,  the  pipes  are  slipped  over 
the  piles  after  they  are  driven.  Between 
the  pile  and  the  pipe  is  then  poured  either  sand  or  concrete. 
These  pipes  rest  on  the  bottom  of  the  river  or  bay,  and  as  the 
teredo,  limnoria,  and  other  marine  wood  borers  never  attack 
timber  below  the  mud  line,  the  pipe  thoroughly  protects 
the  piles.  Although  this  method  of  protection  is  efficient, 
it  has  the  disadvantage  that  broken  pipes  must  be  renewed 
by  placing  new  ones  over  the  head  of  the  piles,  thus 
necessitating  the  removal  of  a  cap  or  other  timber  or  stone 
on  the  pile. 

14.  In  Fig.  8  is  shown  a  section  of  pipe,  patented  by  the 
Lock  Joint  Pipe  Company,  that  overcomes  the  difficulty 
encountered  in  using  ordinary  terra-cotta  pipe.  Cement  and 
sand  or  crushed  stone  are  the  materials  used  in  making  this 


§39 


PILING 


9 


pile  protector,  and,  as  can  be  seen  in  the  illustration,  it  is 
made  in  halves.  Irt  placing  the  pipe  around  the  pile  to  be 
protected,  each  section  is  keyed  with  a  wooden  key  that  has 
been  soaked  in  tar,  and  all  joints  are  securely  sealed  with 
cement.  The  space  between  the  pile  and  the  inside  of  the 
pipe  is  then  filled  with  sand.  The  sand  holds  the  pipe  in 
place,  but  allows  it  to  settle  if  the  bottom  under  the  pipe  is 
scoured  away  by  the  action  of  the  water.  After  the  sand 


Fig.  9 


has  settled  in  place,  the  top  of  the  pipe  is  sealed  with  cement 
to  prevent  the  sand  from  being  washed  out  by  waves  during 
a  storm  or  by  heavy  rains.  Fig.  9  shows  part  of  the  piling 
of  a  trestle  fitted  with  lock-joint  pipe.  If  a  section  of  this 
style  of  pipe  becomes  broken  after  it  is  in  place,  the  broken 
length  is  removed  and  the  pipe  above  is  lowered  into  its  place. 
A  new  section  is  then  placed  at  the  top  to  make  up  the 
required  length. 

211—29 


i 


PILING 


11 


§39 

15.  Piles  driven  in  swamps  or  other  moist  localities  where 
no  marine  wood  borers  are  present  often  fail  by  rotting. 
Creosote  will  lengthen  the  life  of  piles  considerably  in  such 
localities.  The  method  usually  followed,  however,  is  to  cut 
off  the  pile  below  the  water  level  of  the  swamp.  Wood  kept 
wet  all  the  time  will  not  rot.  It  is  only  the  alternate  wet  and 
dry  conditions  that  tend  to  rot  wood.  If  the  piles  are  there¬ 
fore  cut  off  at  a  level  where  they  will  always  be  wet  and  the 
masonry  then  started  from  this  point,  the  danger  from  rotting 
is  eliminated. 

16.  Selection  and  Spacing  of  Piles. — In  ordinary 
soils  that  admit  of  easy  driving,  spruce,  hemlock,  or  short-leaf 
pine  piles  are  used  for  foundation  work.  For  more  compact 
and  harder  soils,  long-leaf,  or  Georgia,  pine,  elm,  or  birch  are 
used.  Where  the  piles  are  not  always  immersed  and  are  sub¬ 
jected  alternately  to  wet  and  dry  conditions,  Georgia  pine, 
palmetto,  or  post  oak  is  employed. 

Wooden  piles  for  building  foundations  should  be  spaced 
not  more  than  30  inches  nor  less  than  20  inches  from  center 
to  center,  and  they  should  be  of  such  a  size  that  the  least 
dimension  at  the  small  end  is  5  inches  and  the  greatest 
dimension  at  the  large,  or  butt,  end  is  12  inches.  The  butt 
end  of  piles  over  20  feet  long  should  be  at  least  20  inches  in 
diameter. 

17.  Capping  of  Piles. — The  several  methods  of  con¬ 
structing  the  capping  of  piles  are  shown  in  Fig.  10.  In  (a)  is 
shown  the  usual  grillage  capping,  which  should  be  of 
hardwood  laid  below  low-water  level  and  composed  of  timbers 
not  less  than  6  inches  thick.  The  crosspieces  a  and  longi¬ 
tudinal  timbers  b  should  be  drift-bolted  to  the  tops  of  the 
piles,  and  the  timber  pieces  should  be  securely  tied  to  each 
other  by  notching  or  by  wrought-iron  straps,  dogs,  or  drift 
bolts.  On  the  top  of  the  grillage  a  flooring  c  of  heavy  planks 
is  placed,  and  the  masonry  is  laid  on  this.  Drift  bolting  con¬ 
sists  in  driving  a  round  bar  of  iron  through  holes  previously 
bored  in  the  timber,  the  holes  having  an  area  somewhat 
smaller  than  the  section  of  the  bar.  However,  they  must 


12 


PILING 


§39 


not  be  so  small  that  the  timbers  will  be  split  in  drifting.  The 
usual  drift  bolt  consists  of  a  1-inch  square  bar  driven  into  a 
J-inch  hole.  The  timber  in  a  grillage  must  be  laid  close  and 
must  have  sufficient  transverse  strength  to  sustain  between 
the  piles  the  several  courses  of  masonry  in  the  footings. 

When  the  foundation  stratum  is  boggy,  the  form  of  timber¬ 
ing  shown  in  view  (6)  is  adopted  in  order  to  protect 
the  wood.  Stout  piles  of  sufficient  length  to  reach  the 
hard  soil  are  driven  along  the  site  and  connected  at  the 
top  by  heavy  timbers  notched  and  spiked  to  them;  these 
are  then  connected  by  similar  timbers  running  crosswise, 
which  are  also  notched  and  spiked  to  those  below.  The 
whole  is  then  embedded  in  concrete  as  shown. 

18.  In  view  (c)  is  shown  the  usual  granite  capping  laid 
on  the  top  of  the  pile.  The  granite  blocks  should  be  dressed 
on  the  bottom,  though  sometimes  they  are  spot-faced;  that  is, 
finished  on  the  small  area  that  bears  on  the  top  of  the  pile. 
The  use  of  granite  capping  makes  possible  a  more  durable 
footing  than  the  use  of  wooden  beam  grillage,  and  it  must  be 
employed  in  cases  where  the  beam  grillage  would  be  above  the 
low-water  line.  Great  care  must  also  be  taken  that  one  pile 
comes  under  each  corner  of  a  stone,  to  keep  it  from  tipping, 
and  that  the  stone  has  a  full  bearing  on  each  pile  head.  To 
insure  this,  the  piles  must  be  sawed  off  perfectly  level  and  all 
the  same  height,  as  no  pieces  of  wood  or  small  bits  of  stone 
should  be  placed  under  the  stones  to  give  them  bearing  on 
the  piles.  Wooden  chips  crush  under  a  load,  and  pieces  of 
stone  are  likely  to  be  broken  or  dislodged,  leaving  the  block 
in  a  state  of  dangerous  instability. 

19.  The  most  satisfactory  capping  for  piles  is  concrete,  as 
shown  in  view  ( d ) .  When  concrete  is  used  it  should  be  placed 
around  the  tops  of  the  piles  to  a  depth  of  at  least  12  inches 
and  should  cover  the  sides  of  the  piles  to  the  same  thickness; 
a  layer  of  concrete  6  inches  thick  should  be  placed  on  top  of 
the  12-inch  layer  to  reinforce  it  further.  Concrete  has  been 
adopted  by  many  engineers  in  preference  to  timber  grillage 
on  account  of  its  durability  and  because  of  the  diminished 


§39 


PILING 


13 


possibility  of  the  footings  slipping  from  the  timber  platform 
by  unequal  settlement.  They  contend  that  slipping  cannot 
occur  with  the  concrete  capping  on  account  of  its  roughness 
and  the  adhesive  surface  that  it  offers  for  the  bed  of  cement 
or  mortar. 


20.  Lateral  Movement  of  Piles. — Where  piles  are 
driven  through  a  yielding  soil  to  the  hard  pan  or  rock  they 
are  likely  to  be  pushed  over  at  the  tops,  moving  about  the 
lower  end  as  a  center.  This  can  hardly  occur  with  piles 
capped  with  concrete,  but  with  a  timber  grillage,  or  platform, 
the  precaution  of  filling  in  around  the  top  of  the  pile  with 
broken  stone  is  often  observed.  Where  this  tendency  toward 
lateral  yielding  is  evident,  a  wall  of  piles  should  be  driven 
around  the  foundation  and  the  piles  carrying  the  foundation 
secured  to  them  by  timber  braces.  Another  method  to  pre¬ 
vent  piles  from  moving  laterally,  though  one  that  is  hardly 
to  be  recommended,  consists  in  securing  tension  braces  or 
guy  lines  to  plates  or  stones  buried  in  the  earth  at  some 
distance  from  the  foundation.  These  guy  lines  or  rods  may 
be  secured  either  to  the  piles  or  to  the  foundation  wall ;  when 
to  the  latter,  they  are  usually  connected  with  an  anchor  that 
is  built  into  the  wall. 


SAND  PILES 


21.  A  sand  pile,  Fig.  11,  is  made  as  follows:  An  ordi¬ 
nary  pile  is  driven  into  the  ground  a  distance  of  5  or  6  feet 
and  then  withdrawn.  This  operation  leaves  a  hole  with  the 
soil  packed  tightly  around  it.  Sand  is 
then  put  into  the  hole,  a  few  inches  at  a 
time,  and  tamped;  then  more  sand  is 
added,  being  tamped  every  few  inches, 
and  so  on  until  the  hole  is  filled.  This 
method  of  piling  is  very  successful  in  soft 
clay.  The  holes  may  be  made  with  an 
auger  instead  of  a  wooden  pile,  although  the  latter  is 
preferable,  as  it  compresses  the  soil  at  the  sides.  The 
bearing  power  of  a  sand  pile  depends  as  much  on  the  friction 


Fig.  11 


14 


PILING 


§39 


against  the  sides,  due  to  the  rubbing  of  the  grains  against 
one  another,  as  on  the  direct  load  carried  to  the  bottom 
of  the  hole. 


METAL  BEARING  PILES 

22.  Cast-Iron  Pile. — In  Fig.  12  is  shown  a  cast-iron 
pile.  This  type  of  pile,  owing  to  its  original  cost  and  the 
difficulty  experienced  in  driving  it,  is  not  extensively 
used. 


23.  Disk  Pile. — The  disk  pile,  Fig.  13,  usually 
consists  of  a  steel  shaft,  or  cylinder,  having  keyed 
to  the  lower  end  a  disk  from  18  to  30  inches  in 
diameter.  This  type  of  pile  is  sunk 
by  washing  away  the  earth  from 
beneath  the  disk  by  a  jet  of  water 
under  pressure.  It  is  used  for  foun¬ 
dations  in  sand  and  for  the  sub¬ 
structure  of  piers  and  wharves. 


24.  Screw  Piles. — As  shown 
in  Fig.  14,  screw  piles  are  those 
which  are  forced  into  the  soil  by 
means  of  a  cast-iron  screw  at  their 
lower  end.  This  screw  is  usually  of 
one  or  two  turns  and  is  securely 
keyed  or  setscrewed  to  the  pile.  Its 
projection  from  the  pile  may  vary 
from  9  to  18  inches,  and  its  pitch 
should  be  from  a  quarter  to  a  half 
of  the  projection.  For  most  require¬ 
ments,  a  screw  having  a  diameter 


Fig.  13 


Fig.  12 

of  from  3§  feet  to  4h  feet  will  be  found  sufficient,  a  sandy 
foundation  requiring  the  larger.  The  shaft  of  the  pile  may 
be  of  Wood  or  of  steel,  usually  the  latter,  in  which  case  it  con¬ 
sists  of  an  extra-heavy  pipe  from  6  to  12  inches  in  diameter. 
The  lower  end  of  the  pipe  is  usually  left  open,  the  edge  being 
beveled,  as  shown  in  (a),  or  provided  with  teeth,  as  shown 


§39 


PILING 


15 


in  ( b ),  to  assist  in  cutting  and  penetrating  the  soil.  Such 
piles  may  be  used  in  most  ordinary  soils,  for  they  will  push 
their  way  through  sand  or  gravel  even  when  it  contains 
boulders  of  some  size.  Hollow  cast-iron  screw  piles  are  fre¬ 
quently  filled  with  concrete  to  strengthen  them  and  to 
increase  the  bearing  surface. 

Screw  piles  are  driven  by  a  capstan  and  levers  fixed  on  the 
top,  and  as  the  pile  descends  lengths  of  pipe  are  added. 
When  the  pile  is  long,  the  shaft  is  made  in  sections  with 


(b) 


(a) 


Fig.  14 


flanged  ends,  which  are  bolted  together,  as  shown  in  (c).  A 
detail  of  the  connecting  bolts  is  shown  in  (d) . 

The  peculiar  advantage  of  the  screw  pile  lies  in  the  fact  that 
it  can  be  used  in  sinking  foundations  adjacent  to  heavy  foot¬ 
ings  that  might  be  damaged  by  driving  common  timber  piles 
with  a  hammer.  It  is  sunk  very  rapidly  through  common  soil 
and  offers  considerable  resistance  to  both  pressure  and  pulling. 


25.  Pneumatic  Piles. — Cylinders,  or  caissons,  of  steel 
or  cast  iron  that  are  sunk  by  excavating  from  the  inside  are 


16 


PILING 


§39 


called  pneumatic  piles.  The  pressure  of  air  maintained 
within  them  prevents  an  influx  of  water.  When  the  piles 
have  been  sunk  to  the  proper  depth  and  the  interior  excavated, 
they  are  filled  with  concrete. 


SHEET  PILES 

26.  Sheet  piling  consists  of  a  wall  of  steel,  reinforced 
concrete,  or  wood  driven  vertically  into  the  ground  at  the 
sides  of  an  excavation.  This  wall  protects  the  adjoining 
property,  sidewalks,  etc.  from  injury  by  the  caving  in  of  the 
bank  during  excavation.  Sheet  piling  is  also  used  to  keep 
back  mud,  sand,  water,  etc.  when  excavating  in  a  wet  place. 


27.  Wooden  Sheet  Piling. — In  Fig.  15  (a)  is  shown  a 
front  elevation  of  plank  slieet  piling.  As  will  be  observed, 
the  piling  a  is  driven  into  the  cellar  bottom  b,  against  the  bank 
of  the  excavation.  In  ( b )  is  a  section  across  the  piling  show¬ 
ing  a  brace  d  placed  against  the  batten  e  to  retain  the  piling 
in  place  and  to  resist  the  pressure  at  the  top.  The  stake 
shown  at  /  is  driven  in  to  keep  the  brace  d  from  slipping. 
These  braces  are  usually  spaced  about  10  or  12  feet  apart, 
and  are  necessary  when  the  excavation  is  a  deep  one. 


§39 


PILING 


17 


The  piles  are  often  pointed  sidewise  as  shown  at  g,  view  (a), 
so  that  each  pile  when  driven  in  will  tend  to  press  against  the 
one  previously  put  in  place. 

If  the  side  pressure  is  not  too  great,  ordinary  plank  from 
3  to  4  inches  thick  will  answer  very  well  for  sheet  piling. 
When  greater  strength  is  required,  square  timbers  may  be 
used,  but  more  frequently  two  or  more  thicknesses  of  plank 
are  employed. 

28.  The  purpose  for  which  sheet  piling  is  used  makes  it 
important  that  the  joints  between  adjoining  piles  be  as  close 


I.  1  <  ^ 

(a)  (c) 


(e)  (f) 


Fig.  16 


(b) 


and  as  nearly  water-tight  as  possible.  Several  devices  for 
securing  this  condition  are  in  use,  a  number  of  them  being 
shown  in  Fig.  16.  In  this  figure,  plain  sheet  piling ,  which 
depends  for  close  joints  on  the  care  and  accuracy  with  which 
it  is  driven,  is  shown  in  (a).  In  ( h )  are  shown  two  contiguous 
rows  of  piling,  one  row  breaking  joints  with  the  other;  three 
rows  of  plank  are  sometimes  used,  the  outside  rows  being  of 
thinner  plank  than  the  central,  or  main,  row.  In  (c),  (d),  (e), 
(/),  and  (g)  are  shown  various  forms  of  tongued-and- grooved 
sheet  piling;  the  object  of  this  construction  is  not  only  to 
make  a  tight  joint,  but  also  to  assist  in  guiding  the  piles  truly 


18 


PILING 


§39 


in  the  same  plane.  The  form  shown  in  (d)  is  very  frequently 
used,  the  tongue  and  groove  being  formed  by  spiking  narrow 
strips  on  the  edge  of  the  pile.  The  form  in  (g)  is  a  patented 
form  known  as  the  Wakefield  pile;  its  construction  is  evident 
from  the  figure  without  further  description.  The  points  of 
sheet  piles  are  usually  sharpened  to  facilitate  driving,  and 
one  side  is  often  sloped,  as  shown  in  ( h ),  to  cause  the  piles 
to  come  into  close  contact  with  one  another,  as  already 
mentioned. 


29.  Wooden  sheet  piling  is  sometimes  made  sufficiently 
tight  to  resist  the  percolation  of  water  by  placing  back  of  it 


Fig.  17 


a  12-  or  18-inch  puddle  wall  of  clay  well  tamped  in  place.  In 
driving  sheet  piling,  the  planks  and  timbers  should  be  driven 
between  guides  that  are  bolted  to  a  frame  properly  supported 
and  secured  to  posts  or  timber  piles  at  frequent  intervals,  as 
shown  in  Fig.  17. 

30.  Steel  Slieet  Piling. — There  are  on  the  market 
several  designs  of  steel  slieet  piling.  Steel  sheet  piling 
has  several  advantages  over  wooden  sheet  piling:  It  is  easier 
to  drive;  it  is  stronger;  it  will  last  longer;  it  may  be  used  more 
than  once;  and  when  it  is  worn  out,  it  can  be  sold  as  scrap 
and  made  into  new  piling,  whereas  worn-out  wooden  piling 
cannot  be  used  for  anything  except  firewood. 


§39 


PILING 


19 


31.  The  Nye  Interlocking  piling,  which  consists 
of  ordinary  structural-steel  channels,  is  illustrated  in  Fig.  18. 
The  pile,  or  channel,  a  is  driven  into  the  ground  until  it  is 
firmly  in  place.  The  second  pile  b  is  then  placed  in  position 
beside  it.  On  the  bottom  of  this  second  pile  is  placed  a  clip  c 
that  engages  with  the  flange  of  the  pile  a  and  holds  the  two 
piles  together  at  the  lower  end.  A  clip  d  is  also  placed  on  the 
top  of  the  pile  a.  This  clip  engages  with  the  flange  of  the 
pile  b,  serving  to  guide  it  at  the  top  while  it  is  being  driven. 


When  the  pile  b  is  descending  the  clip  c  sinks  with  the  pile, 
and  the  clip  d  remains  stationary  on  top  of  the  pile  already 
driven. 

In  actual  work,  often  the  pile  a  is  driven,  the  clip  c  is  slid 
over  its  flange,  and  the  clip  d  is  put  in  place.  The  pile  b  is 
then  lowered  in  place,  engaging  with  the  clip  d  and  the  top 
of  the  clip  c.  In  the  illustration,  the  third  pile  e  is  shown 
partly  driven. 

Clips  are  also  made  of  such  shape  that  I  beams  may  be  used 
as  piles  instead  of  channels  if  desired;  but  this  change  makes 


20 


PILING 


§39 


the  piling  quite  heavy.  They  are  also  made  so  that  a  wooden 
filler  may  be  driven  in  between  the  channels  or  beams.  This 
filler  makes  the  piling  water-tight  when  it  is  to  be  used  in  wet 
places.  Such  an  arrangement  is  shown  in  Fig.  10,  where  the 
wood  filler  is  shown  at  a. 


Fig.  19 


After  the  piling  has  served  its  purpose,  it  may  be  with¬ 
drawn,  and  used  over  again.  It  is  generally  in  such  good  con¬ 
dition  after  being  employed  once  or  twice  as  piling  that  it 
can  be  used  subsequently  in  the  construction  of  floors  or 
columns  in  buildings. 


§  39 


PILING 


21 


32.  Another  style  of  patented  steel  sheet  piling,  known 
as  the  Jackson  piling,  is  shown  in  Fig.  20.  This  piling 


is  made  up  of  structural-steel  I  beams  and  channels.  The 
channels  are  bolted  together  in  pairs  and  are  driven  together. 
Sometimes  the  spaces  between  each  pair  of  channels,  as  at  a, 
are  filled  with  clay  so  as  to  make  the  sheeting  water-tight. 
This  kind  of  piling  is  strong  and  is  good  for  heavy  work. 

33.  In  Fig.  21  is  shown  the  Friestedt  interlock¬ 
ing  channel- bar  piling.  To  the  channels  are  riveted 


Fig.  21 

Z  bars  a  to  act  as  guides  for  the  adjacent  channels.  In  light 
work,  instead  of  using  continuous  Z  bars  to  lock  the  channels 


22 


PILING 


§39 


together,  short  lengths  of  Z  bars,  or  “clips,”  are  used  at 
intervals  of  about  2  feet  to  hold  the  channels  in  place.  When 
very  heavy  work  is  required,  the  number  of  Z  bars  is  doubled. 
In  ordinary  construction,  two  Z  bars  are  riveted  to  every 
other  channel.  When  the  double-locked  piling  is  used, 
however,  there  are  two  Z  bars  riveted  to  every  channel. 
The  extra  set  is  put  on  exactly  in  the  same  relative  position 
as  the  first  set.  One  of  the  Z  bars  of  the  extra  set  is  shown 
dotted  at  b.  The  hole  at  the  top  of  each  pile  is  of  use  when 
it  is  desired  to  withdraw  the  pile. 

34.  The  steel  sheet  piling  so  far  described  consists  of 
structural  steel  shapes  that  can  be  bought  in  the  open  market. 


Fig.  22 

There  are,  however,  makes  of  steel  sheet  piling  composed  of 
specially  rolled  shapes.  An  example  of  this  style  of  piling 
is  shown  in  Fig.  22,  which  illustrates  what  is  known  as  United 
States  steel  slieet  piling.  About  G5  per  cent,  of  the 
piling  used  today  is  of  this  make.  As  can  be  seen,  all  the 
piles  are  alike  and  require  no  special  clips  riveted  to  them 
as  do  many  other  makes.  It  is  not  so  strong  laterally  as  some 
of  the  styles  of  piling  previously  described,  but  it  has  one 
marked  advantage,  namely,  that  the  design  of  the  piling 
readily  lends  itself  for  use  along  curved  lines,  on  even 
quite  sharp  angles,  without  the  necessity  of  special  piles. 
When  a  sharp  turn  is  to  be  made,  the  pile  that  is  to  be  located 
at  the  angle  is  bent  to  the  required  shape. 


§39 


PILING 


23 


35.  Another  style  of  sheet  steel  piling  that  gives  satis¬ 
factory  results  is  the  Wemlinger  piling,  an  illustration  of 
which  is  shown  in  Fig.  23.  It  consists  simply  of  heavy, 
corrugated  steel  plates.  Each  plate  consists  of  about  two 
and  one-half  complete  corrugations.  On  each  plate  is  a 
plate  a,  which  acts 
as  a  guide  for  the 
adjacent  plates.  The 
plates  lap  each  other 
to  such  an  extent  that 
the  metal  is  practi¬ 
cally  double  thickness 
all  over.  The  guide 
plate  a  comes  to  with¬ 
in  about  1  inch  of  the 
top  of  the  pile  proper. 

If  it  were  made  flush 
with  the  piling,  the 
blow  of  the  pile  driver 
might  fall  entirely  on 
the  guide  plate  in¬ 
stead  of  on  the  pile 
proper,  in  which  case  the  rivets  that  hold  these  parts 
together  would  likely  be  sheared. 

This  style  of  piling  has  more  strength  for  the  amount  of 
metal  used  than  steel  sheet  piling  made  from  structural 
shapes.  When  it  is  desired  to  make  a  right  angle  turn  in  the 
piling,  the  metal  is  simply  bent  to  the  required  angle. 


METHODS  OF  DRIVING  PIEES 

36.  Piles  of  small  size  that  are  to  be  driven  only  com¬ 
paratively  short  depths  may  be  forced  into  position  by  means 
of  sledges  or  mauls  in  the  hands  of  workmen.  Screw  piles 
are  driven  into  the  soil  in  the  same  manner  as  wood  screws 
are  forced  into  wood.  As  previously  stated,  disk  piles  are 
sunk  with  a  water  jet.  Some  forms  of  concrete  piles  are 
sunk  by  special  methods,  which  will  be  spoken  of  later. 


24 


PILING 


v 


§39 


Large  common  piles,  however,  are  almost  invariably  sunk 
by  a  machine  called  a  pile  driver.  There  are  two  kinds 
of  pile  drivers  in  common  use,  namely,  the  drop-hammer  pile 
driver  and  the  steam-hammer  pile  driver. 

37.  Drop-Hammer  Pile  Drivers. — Fig.  24  illustrates 
a  very  common  type  of  drop-hammer  driver.  It  consists 
essentially  of  a  heavy  weight  a,  called  the  hammer ,  and  of 
motive  power  and  mechanism  for  raising  the  hammer  and 


allowing  it  to  fall  on  the  top  of  the  pile.  The  hammer  is 
usually  of  cast  iron,  of  the  form  shown  in  (a),  and  weighs 
from  1,000  to  3,000  pounds.  It  is  cast  with  vertical  grooves, 
or  recesses,  a',  which  partly  envelop  and  engage  with  the 
upright  guides  b,  called  the  leads.  These  are  two  timbers 
supported  on  a  horizontal  platform,  and  serve  to  guide  the 
hammer  in  its  vertical  motion.  The  leads  are  braced  and 
stiffened  by  inclined  struts  c.  A  line  r  of  rope  or  wire  cable 
has  one  of  its  ends  attached  to  the  hammer,  from  which 
it  passes  over  a  sheave  at  the  top  of  the  leads  and  thence  to 


§39 


PILING 


25 


the  drum  d  of  a  hoisting  engine.  This  drum  is  connected 
to  the  engine  through  a  friction  clutch,  by  which  it  may  be 
quickly  thrown  into  and  out  of  gear.  Another  drum  dl  simi¬ 
larly  connected  to  the  engine  operates  a  second  cable  rx 
passing  over  a  sheave  at  the  top  of  the  leads  and  used  for 
hoisting  the  pile  into  place. 

38.  In  operation,  the  hammer  is  raised  out  of  the  way, 
and  the  pile  is  hoisted  and  placed  upright  between  the  leads, 
with  its  foot  on  the  ground  where  it  is  to  be  driven,  and 
secured  in  position  by  appropriate  devices.  The  hammer  is 
gradually  lowered  on  the  head  of  the  pile,  to  force  the  latter 
into  the  ground  to  a  slight  depth,  dependent  on  the  softness 
of  the  soil.  The  ham¬ 
mer  is  then  raised  to 
any  desired  height, 
the  engine  stopped, 
and  the  friction  clutch 
released,  when  the 
hammer  drops  on  the 
head  of  the  pile.  In 
doing  so,  it  draws  the 
cable  with  it,  revers¬ 
ing  the  motion  of 
the  drum,  which  is 
partly  controlled  by  a  brake  that  prevents  it  from  continu¬ 
ing  to  revolve  after  the  hammer  has  struck  the  top  of  the 
pile.  This  operation  is  repeated  until  the  pile  is  driven  to 
the  desired  depth.  Sometimes  a  cushion,  made  usually  of 
a  block  of  wood,  is  placed  on  the  head  of  the  pile.  This  pre¬ 
vents  the  hammer  from  striking  directly  on  the  pile,  an 
operation  that  is  liable  to  injure  the  head  of  the  pile.  When 
driving  steel  sheet  piles,  a  cast-iron  cushion,  or  driying  cap, 
is  often  used. 

4 

39.  The  method  just  described  of  attaching  the  hoisting 
line  permanently  to  the  hammer  is  the  one  now  most  com¬ 
monly  used,  and  is  considered  the  most  satisfactory.  Some 

machines  are,  however,  still  equipped  with  an  automatic 
211—30 


Fig.  25 


26 


PILING 


§39 


catch,  called  a  “nipper,”  between  the  end  of  the  line  and  the 
hammer.  This  device  is  illustrated  in  Fig.  25.  The  nippers 
proper  b  are  attached  to  a  cross-beam  a  that  has  recesses 
at  its  ends  and  slides  up  and  down  on  the  leads.  The 
line  is  attached  to  an  iron  piece  having  an  eye  at  its  top,  as 
shown.  To  the  top  of  the  hammer  is  attached  a  clevis  having 
a  wedge-shaped  crosspiece  d  between  the  sides.  When  the 

nippers  are  lowered,  they  slide  over  this 
wedge-shaped  piece  and  engage  with  it;  and 
when  the  line  is  hoisted,  it  carries  the  ham¬ 
mer  with  it.  At  the  top  of  the  leads  are 
placed  tripping  blocks,  which  press  the  curved 
arms  together,  thus  releasing  the  hammer. 
The  line  is  then  lowered,  the  nippers  again 
engage  the  hammer,  and  the  operation  is 
repeated.  This  device  is  seldom  used  now 
except  with  small  drivers  operated  by  horses. 

40.  Steam-Hammer  Pile  Drivers. 
A  steam-hammer  pile  driver  differs  from 
a  drop-hammer  machine  in  that  the  hammer 
is  operated  by  steam,  in  the  same  general  way 
as  the  steam  hammers  used  for  forging  iron 
and  steel.  The  mechanism  consists  of  a 

vertical  steam  cylinder  with  a  piston  having 

\ 

a  stroke  of  about  3  feet,  the  lower  end  of  the 
piston  rod  carrying  a  heavy  hammer. 
Fig.  26  illustrates  the  construction  of  the 
steam  hammer,  though  the  machines  in 
actual  use  are  more  elaborate.  At  a  is 
shown  the  steam  cylinder;  at  b,  the  piston 
rod;  at  c,  the  hammer;  and  at  d,  the  guides,  the  upper  ends 
of  which  are  attached  to  the  steam  cylinder,  and  the  lower 
ends  to  the  anvil  block  or  plate  e.  These  rods  pass  through 
holes  in  the  sides  of  the  hammer,  thus  guiding  its  motion. 
The  block  e  has  a  conical  hole  through  its  center,  as  shown 
by  dotted  lines,  and  the  hammer  has  a  projection  /  that  passes 
freely  through  this  opening. 


Fig.  26 


§39 


PILING 


27 


Steam,  conveyed  to  the  cylinder  by  a  flexible  pipe  or  hose, 
is  admitted  below  the  piston,  forcing  it  and  the  attached 
hammer  upwards.  At  the  end  of  the  upward  stroke,  the 
steam  is  automatically  cut  off,  the  exhaust  port  is  opened, 
and  the  hammer  and  piston  fall  by  their  own  weight  to  their 
original  position;  steam  is  again  automatically  admitted,  and 
the  operation  repeated.  The  whole  mechanism  is  placed 
between  and  guided  by  the  leads,  and  is  suspended  by  the 
line  that,  in  the  drop-hammer  machine,  carries  the  hammer. 
When  the  pile  is  in  place,  the  whole  apparatus  is  lowered  on 
its  top,  which  is  usually  dressed  to  fit  approximately  the 
conical  hole  in  the  anvil  block.  Steam  is  then  turned  on  and 
the  hammer  begins  to  work,  striking  rapid  blows  and  follow¬ 
ing  the  pile  as  it  descends. 

41.  Comparison  of  Drop-  and  Steam-Hammer  Pile 
Drivers. — There  has  been  much  discussion  as  to  the  com¬ 
parative  merits  of  the  two  types  of  pile  drivers  just  described. 
The  truth  is  that  each  is  most  effective  under  conditions  that 
favor  its  use.  In  the  drop-hammer  machine,  the  hammer 
may  be  allowed  to  fall  any  distance  from  1  to  30  or  more  feet; 
while  in  the  steam  hammer  the  fall  is  limited  to  the  stroke  of 
the  piston,  usually  from  2\  to  3^  feet.  As  with  other  falling 
bodies,  the  energy  developed  by  the  drop  of  the  hammer  is 
measured  by  the  product  of  the  weight  and  the  distance 
through  which  it  falls.  With  hammers  of  equal  weight,  it 
is  obvious  that  the  drop  hammer,  with  its  much  greater 
possible  range  of  fall,  is  capable  of  delivering  the  more  ener¬ 
getic  blows,  and  is  therefore  more  effective  where  the  material 
to  be  penetrated  is  very  hard.  On  the  other  hand,  the  steam 
hammer  delivers  its  blows  much  more  rapidly  than  the  drop 
hammer,  and,  if  the  material  through  which  the  piles  are  to 
be  driven  is  comparatively  soft,  so  that  the  energy  of  the  blow 
is  adequate  to  force  the  pile  through  it,  more  rapid  progress 
may  be  made  than  with  the  drop  hammer. 

As  is  well  known,  if  a  pile  is  partly  driven  one  day  and  then 
driven  full  depth  the  next  day,  more  power  will  be  required 
to  drive  the  pile  on  the  second  day  than  would  be  the  case  if 


28 


PILING 


§39 


it  had  not  been  allowed  to  stand  overnight.  This  is  due  to 
the  mud  and  other  soft  material  through  which  the  pile  is 
driven  settling  around  it.  The  advocates  of  the  steam 
hammer  claim  that  the  blows  are  delivered  on  the  head  of 
the  pile  so  fast  that  the  pile  never  becomes  entirely  still,  but 
is  continually  vibrating  or  moving  forwards. 

In  practice,  the  steam  hammer  is  made  from  25  to  50  per 
cent,  heavier  than  the  drop  hammer,  and  this  partly  compem 
sates  for  the  smaller  fall  of  the  former.  The  greater  energy 
of  the  blow  of  the  drop  hammer,  where  it  is  not  required  to 
force  the  pile  through  hard  material,  is  disadvantageous, 
because  it  is  much  more  likely  to  split,  or  broom,  the  head 
of  the  pile.  On  the  other  hand,  the  first  cost  of  the  steam- 
hammer  outfit  is  much  greater  than  that  of  the  drop  hammer, 
and  its  more  complicated  mechanism  makes  it  more  liable 
to  break  down  and  more  expensive  to  keep  in  repair.  The 
drop-hammer  machine  is  preferred  by  almost  all  contractors. 

42.  Driving  of  Inclined  Piles. — Piles  are  usually 
driven  vertically.  When,  in  exceptional  circumstances,  it 
is  necessary  to  have  them  inclined,  this  is  done  by  simply 
inclining  the  leads  of  the  pile  driver. 

43.  Location  of  Pile  Drivers. — For  building  and  other 
similar  work,  the  pile-driving  mechanism  is  installed  on  the 
ground,  near  the  place  where  the  piles  are  to  be  driven.  When 
piles  are  to  be  driven  in  water,  the  pile  driver  is  placed  on  a 
flatboat,  or  scow,  so  that  it  can  be  readily  moved  from  point 
to  point.  Pile  drivers  for  work  on  operating  railroads  are 
placed  on  flat  cars  in  such  a  manner  that  they  can  be  revolved 
in  a  horizontal  plane,  thus  allowing  the  leads  to  be  swung 
through  a  considerable  arc  from  side  to  side,  in  order  to  drive 
the  piles  in  any  position  required.  Drivers  are  also  con¬ 
structed  so  that  the  leads  can  be  inclined  to  drive  the  outer, 
or  batter;  piles  at  the  proper  angle  with  the  vertical. 


§30 


PILING 


29 


STRENGTH  OF  PILES 


SHEET  PILING 

44.  Sheet  piling  is  usually  driven  without  any  calculation 
as  to  whether  it  will  be  strong  enough  or  not,  the  chief  require¬ 
ment  being  that  it  shall  be  practically  water-tight.  If  it  is 
found  that  the  piling  is  not  strong  enough  to  hold  back  the 
water  or  soft  mud,  shores  serving  as  braces  are  placed  on  the 
inside  of  the  work.  A  sufficient  number  of  shores  or  braces 
are  used  to  insure  the  requisite  strength.  Sometimes,  instead 
of  using  braces,  two  sets  of  sheet  piling  are  driven  about 
2  feet  apart  and  the  space  between  them  is  then  filled  with 
clay,  provided  they  are  driven  in  water.  This  method 
insures  a  stronger  job  and  at  the  same  time  one  that  is  more 
nearly  water-tight. 


BEARING  PILES 

45.  It  is  well  before  discussing  the  calculation  of  the 
bearing  power  of  piles  to  investigate  the  causes  that  assist 
their  stability.  There  are  three  causes  that  contribute  to  the 
bearing  power  of  piles. 

46.  First,  the  piles  are  often  driven  through  soft  stratum 
to  a  harder  underlying  stratum.  Thus,  piles  are  often  driven 
through  soft  mud  or  quicksand  to  hard  pan  or  bed  rock. 
In  such  cases,  each  pile  simply  acts  as  a  column ;  one  end  rests 
on  the  rock  and  the  superstructure  is  carried  at  its  top.  Of 
course,  the  bearing  of  the  pile  on  the  rock  will  as  a  rule  not 
have  a  bed  that  is  as  smooth  and  regular  as  a  wooden  column 
in  a  building  would  have.  On  the  other  hand,  the  pile  is  sup¬ 
ported  to  a  certain  extent  laterally  by  the  soft  material  . 
through  which  it  is  driven,  and  in  this  respect  would  be 
stronger  than  a  wooden  column  in  a  building. 

It  often  happens  that  the  bed  rock  or  hard  pan  is  so  far 
below  the  surface  of  the  ground  that  it  is  impracticable  or 
even  impossible  to  drive  piles  down  to  it.  In  such  a  case, 


30 


PILING 


§39 


this  first  cause  contributing  to  the  bearing  power  of  piles  is 
entirely  lost,  and  the  other  two  causes  to  be  mentioned  must 
be  relied  upon  entirely  for  strength  and  stability. 

i 

47.  The  second  cause  of  the  stability  of  a  pile  is  due  to 
the  friction  against  its  sides  of  the  material  through  which  it 
is  driven.  The  mud,  quicksand,  or  other  similar  material 
presses  on  the  sides  of  the  pile  and  thus  holds  it  in  place. 
The  particles  of  mud  settle  more  compactly  around  the  pile 
all  the  time,  so  that  the  longer  a  pile  has  been  driven  the  more 
firmly  it  is  held  in  place.  An  actual  case  on  record  shows 
that  thirty-five  piles  easily  driven  in  soft  mud  required  a  load 
of  130,000  pounds  to  start  them  after  being  in  place  24  hours. 
In  another  case,  a  52-foot  pile  13  inches  in  diameter  was 
driven  with  a  4,200-pound  steam  hammer  in  material  so  soft 
that  the  last  blow  of  the  hammer  sunk  the  pile  6  inches.  On 
the  following  day  the  pile  carried  a  load  of  51  tons  without 
settlement  and  had  developed  a  frictional  resistance  of 
15  pounds  per  square  inch  of  surface.  It  is  this  friction  of  the 
material  through  which  the  pile  is  driven,  on  the  sides  of  the 
pile  itself,  that  is  frequently  the  most  potent  factor  in  holding 
the  pile  in  place. 

It  is  claimed,  as  has  been  already  suggested,  that  a  pile 
driver  that  strikes  blows  rapidly  will  drive  a  pile  farther  at 
each  blow  than  one  that  strikes  blows  more  slowly,  for  in 
between  the  rapid  succession  of  blows  the  pile  has  not 
reached  a  state  of  actual  rest  and  the  material  surrounding 
it  has  not  had  time  to  settle  in  place.  It  is  customary  to 
calculate  the  bearing  strength  of  a  pile  from  the  distance  it 
sinks  at  the  last  blow  of  the  hammer.  Therefore,  as  the 
pile  has  a  greater  bearing  capacity  than  this  on  the  following 
month,  or  even  the  following  day,  it  can  be  seen  that  the 
formulas  for  calculating  the  strength  of  piles  will  err  on  the 
side  of  safety. 

48.  The  third  cause  of  the  stability  of  piles  is  due  to  the 
fact  that  the  pile,  as  it  is  driven,  must  make  room  for  itself 
and  therefore  compress  the  soil  in  its  vicinity.  This  com¬ 
pression  of  the  soil  has  two  effects:  (1)  it  causes  the  soil  to 


§39 


PILING 


31 


taken  from  an  actual  example,  is  shown  a  Simplex  concrete 
pile,  which  will  be  described  later,  from  around  which  part 
of  the  earth  has  been  excavated,  so  as  to  disclose  the  several 
strata,  or  layers,  of  soil  through  which  the  pile  passes.  As 
will  be  observed,  the  strata  of  earth  are  forced  together  by  the 
penetration  of  the  pile  form.  It  is  thus  evident  that  if  piles 


press  more  forcefully  against  the  sides  of  the  pile,  which  causes 
more  friction;  and  (2)  the  soil  between  the  piles,  by  being  com¬ 
pressed,  will  hold  more  weight. 

The  manner  in  which  the  soil  is  compressed  from  the  oper¬ 
ation  of  driving  is  shown  in  Fig.  27.  In  this  illustration, 


Fig.  27 


32 


PILING 


§  39 


are  driven  at  close  intervals,  they  will  greatly  improve  the 
bearing  value  of  the  soil  surrounding  them  and  permit  it  to 
be  used  for  ordinary  loads,  even  if  they  do  not  bear,  at  their 
lower  end,  upon  hard  pan,  gravel,  or  bed  rock.  An  analysis 
of  Fig.  27  will  show  that  the  effect  of  the  compression  of  the 
soil  by  the  driving  of  the  pile  extends  for  a  distance  about 
equal  to  the  diameter  of  the  pile  on  all  sides. 

49.  Formulas. — Piles  driven  to  bed  rock  through  a 
compact  soil  are  not  likely  to  fail  by  deflection,  but  will  fail 
by  crushing.  The  pile  may  then  be  proportioned  to  the  allow¬ 
able  resistance  to  crushing  at  the  minimum  section,  but  a 
factor  of  safety  of  at  least  6  should  be  used.  The  building 
laws  in  several  of  the  largest  cities,  however,  stipulate  that 
no  pile  shall  be  loaded  in  excess  of  40,000  pounds. 

Piles  when  not  driven  to  hard  pan  or  bed  rock  depend  for 
their  bearing  value  on  the  bearing  value  of  their  ends,  and 
principally  on  the  frictional  resistance  between  their  sides 
and  the  soil.  The  bearing  value  of  piles  not  driven  to  bed 
rock  is  difficult  to  determine.  Many  rules  and  formulas  have 
been  evolved  and  the  best  are  founded  on  practical  data 
obtained  by  experiment,  but  they  vary  greatly  and  the  engi¬ 
neer  must  choose  the  one  that  seems  most  nearly  to  agree 
with  his  experience.  The  following  formula,  which  is  known 
as  the  Engineering  News  formula,  is  used  in  the  best 
practice  and  is  recommended  by  the  building  laws  of  several 
cities: 


2  PH 
a+  1 


in  which  14^  =  safe  load,  in  tons,  or  bearing  value  of  pile; 

P  =  weight  of  hammer,  in  tons; 

H  =  fall  of  hammer,  in  feet ; 

a  =  penetration  of  pile,  in  inches,  produced  by  last 
blow  of  hammer. 


When  the  formula  is  to  be  used  for  a  steam  pile  driver  the 

denominator  is  changed  from  a  +  1  to  a  +  .  1 . 

* 

The  penetration  of  the  pile  under  the.  last  blow  is  con¬ 
siderably  affected  if  the  head  is  broomed,  or  splintered,  in 


§39 


PILING 


33 


driving,  and  in  order  to  obtain  correct  results  when  driving 
test  piles,  these  broomed  heads  should  be  removed  before  the 
last  blow  is  struck.  Many  engineers  call  the  penetration  of 
the  pile  at  the  last  blow  the  refusal.  Thus,  a  statement  to  the 
effect  that  a  pile  is  driven  to  a  refusal  of  ^  inch  with  a  certain 
hammer,  means  that  the  penetration  at  the  last  blow  was 
\  inch. 

Example. — In  driving  the  piles  for  the  foundation  of  a  large  build¬ 
ing,  the  penetration  is  ^  inch  under  the  last  blow  of  a  1-ton  hammer. 
What  will  be  the  allowable  bearing  value  of  the  pile,  figured  accord¬ 
ing  to  the  formula  just  given,  provided  the  hammer  falls  15  feet? 

Solution. — In  the  formula,  the  safe  bearing  value  of  the  pile  is 

IPp  — ~r^~»  and,  by  substitution,  =  =20  T.  Ans. 

p  a  + 1  p  .5  +  1 


EXAMPLES  FOR  PRACTICE 

1.  What  will  be  the  safe  bearing  value  of  a  timber  pile  that  under 

the  last  blow  of  a  H-ton  hammer  has  a  penetration  of  1  inch,  the  fall 
of  the  hammer  being-  12  feet?  Ans.  18  T. 

2.  A  pile  driven  through  stiff  clay  has  a  penetration  of  2  inches 

under  the  last  blow  of  a  hammer  weighing  1,000  pounds  and  falling 
through  a  distance  of  14  feet.  What  will  be  the  allowable  bearing 
value  of  the  pile?  Ans.  4.7  T. 


50.  Table  I  gives  a  collection  of  several  of  the  principal 
formulas  employed  to  determine  the  bearing  value  of  timber 
piles  driven  by  a  hammer,  although  the  one  given  in  the  pre¬ 
ceding  article  agrees  more  nearly  than  most  of  them  with  the 
actual  tests  made  on  piles,  except  possibly  the  one  evolved 
from  experiments  by  Hertiz. 

In  the  formulas  given  in  the  table,  p  =  penetration  of  pile, 
in  feet,  under  last  blow,  and  W  =  ultimate  bearing  value  of 
pile,  in  tons.  The  other  letters  have  the  same  value  as  those 
in  the  preceding  article. 

51.  Factor  of  Safety. — Some  of  the  formulas  of  Table  1 
give  the  safe  load  that  a  pile  will  carry,  while  the  others  give 
the  ultimate  load.  With  the  formulas  giving  the  ultimate 
load,  a  factor  of  safety  must,  of  course,  be  used.  With  some 


34 


PILING 


§39 


pile  work,  for  example,  a  temporary  railroad  trestle,  a  slight 
settlement  makes  no  great  difference;  but  with  building 
operations  the  settlement,  particularly  if  not  uniform,  is 
disastrous.  For  this  reason,  a  large  factor  of  safety  should 
be  used.  A  factor  of  from  4  to  10  is  usually  employed per¬ 
haps  7  might  be  considered  sufficient  as  a  general  rule. 

52.  Bearing  Power  of  Screw  and  Disk  Piles. — There 
is  no  rule  by  which  the  bearing  power  of  screw  and  disk  piles 

TABLE  I 


EMPIRICAL  FORMULAS  FOR  DETERMINING  THE  BEARING 
VALUE  OF  TIMBER  PILES  DRIVEN  BY  HAMMER 


Authority 

Formulas 

T  raiitwine 

Baker . 

I  +  I  2  p 

W  —  ioo[V-P  H  +  $o(p)2  —  50  p] 

Sander . 

w  PH 

Nv  strom . 

P  8  p 

W  =  lPH 

Hertiz . 

p 

W=  V500  P  H+  (250  p)2—  250  p 

may  be  determined.  Where  possible,  it  is  better  to  test  one 
pile  on  the  job  and  then  use  a  working  load  not  over  one-fourth 
the  ultimate  load.  Where  this  cannot  be  done,  the  load  that 
the  pile  will  carry  is  merely  a  matter  of  experience.  As  a 
rule,  a  disk  or  a  screw  pile  will  settle  under  a  load  of  from 
1  to  8  tons  per  square  foot  of  bearing  area,  depending  on  the 
soil  into  which  it  is  driven.  The  value  of  1  ton  given  as  a 
minimum  is  very  rarely  experienced ;  indeed,  it  is  usually  safe 
to  use  a  working  load  of  from  1  ton  to  \\  tons  per  square  foot 
of  bearing  surface. 


§39 


PILING 


35 


CONCRETE  PILING 


INTRODUCTION 

53.  Methods  of  Constructing  Concrete  Piles. 
Concrete  piles  may  be  constructed  primarily  in  two  ways: 
(1)  by  forming  the  pile  in  the  ground,  and  (2)  by  molding  the 
pile,  allowing  the  concrete  to  set,  and  afterwards  driving  it 
into  the  ground  with  a  hammer  or  some  other  means. 

There  are  several  patented  methods  for  constructing  con¬ 
crete  piles  by  the  first  process,  the  methods  being  the  basis 
for  the  patents,  but  no  patents  cover  the  construction  of 
molded  concrete  piles  of  ordinary  form  that  are  driven  by  a 
steam  hammer  or  a  water  jet.  Such  piles  may  be  designed 
and  reinforced  to  suit  the  conditions  of  construction. 

54.  Advantages  of  Concrete  Piles.— Concrete  piles 
have  many  advantages  over  timber  piles,  the  principal  ones 
being  that  they  are  more  durable  and  that  they  will  sustain  a 
greater  load.  In  timber-pile  construction,  it  is  necessary  to 
cut  the  piles  below  high-water  level,  as  otherwise  they  will 
deteriorate  and  decay  rapidly.  Such  is  not  the  case  with 
concrete  piles,  as  they  are  durable  under  all  conditions  of 
exposure.  The  one  serious  objection  to  timber  piles,  which  is 
overcome  by  the  use  of  concrete  for  pile  construction,  con¬ 
sists  in  the  fact  that  they  are  attacked  and  destroyed  by 
marine  wood  borers;  consequently,  concrete  piles  are  greatly 
superior  for  construction  work  where  driven  in  sea-water,  as 
they  are  immune  from  such  attacks. 

Generally,  concrete  piles  will  safely  sustain  a  load  at  least 
twice  as  great  as  timber  piles  will  support,  so  that  while  their 
cost  is  considerably  in  excess  of  timber  piles,  fewer  of  them 
will  be  needed.  If  the  concrete  pile  is  molded  in  the  ground, 
it  is  not  unusual  for  the  surrounding  earth  to  become  per- 


*  * . *  • '.  *•  *.***'  . .  *  *  •  •**  *  *  •  •  •*.*■*' 


A  ^  <7.  *7  .  .<? v-7  yv  v  ?  A&y i  A^>1 


■<7 


m§mmm 


V  A 

M 


Fig.  28 


36 


§39 


PILING 


37 


meated  with  the  cement  to  a  considerable  extent,  thus  improv¬ 
ing  the  character  of  the  soil  and  increasing  the  bearing  strength 
of  the  pile.  Another  advantage  of  concrete  piles  over  wooden 
piles  is  that  they  may  be  reinforced,  and  the  reinforcement 
embedded  in  them  may  interlace  with  the  reinforcement  of 
the  footing  or  capping  in  such  a  way  as  to  provide  an  anchor¬ 
age  for  steel  chimneys,  tank  towers,  and  other  tall  structures 
subjected  to  wind  pressure.  Concrete  piles  are  also  less  likely 
to  be  damaged  when  driven  and  finished  than  are  wooden 
or  timber  piles. 

55.  Soils  Best  Suited  for  Concrete- Pile  Construc¬ 
tion.  —  Concrete  piles  can  frequently  be  used  advan¬ 
tageously  to  provide  for  foundations  of  buildings  to  be 
erected  upon  a  site  overlaid  with  soft  clay,  mud,  or  strata 
of  quicksand  or  other  soil  of  doubtful  bearing  value.  By 
their  use  a  saving  in  cost,  as  well  as  in  time,  over  the  old 
method  of  excavating  and  then  erecting  concrete  piers  is 
frequently  possible.  Referring  to  Fig.  28,  the  columns  in 
both  (a)  and  (6)  support  the  same  load.  In  (a)  is  shown  the 
usual  method  of  penetrating  a  soft  clay  and  muddy  soil  in 
order  to  carry  the  foundations  down  to  the  gravel  or  hard  pan, 
while  in  ( b )  the  same  column  is  shown  supported  upon  con¬ 
crete  piles.  From  view  (a)  it  is  evident  that  a  considerable 
amount  of  excavating  is  necessary  before  the  concrete  pier 
can  be  constructed.  As  is  usually  the  case  with  soft  clay  soil, 
the  cost  of  excavation  is  increased  by  the  pumping  necessary 
to  keep  the  excavation  free  from  water,  and,  in  addition,  a 
large  quantity  of  concrete  is  required  to  build  from  the  hard 
pan  to  the  top  of  the  foundation  to  provide  the  necessary 
strength;  there  is  also  danger  attached  to  excavating  in  this 
manner  on  account  of  the  possibility  of  slides  and  caves. 
With  the  use  of  concrete  piles,  all  these  difficulties  are  over¬ 
come,  and  it  is  best  to  use  concrete-pile  construction  even  at 
a  slight  increase  in  cost,  on  account  of  the  time  that  may  be 
saved.  The  concrete  piles  in  Fig.  28  ( b )  could  probably  be 
driven  in  one-fourth  the  time  it  would  take  to  make  the 
excavation  and  fill  in  the  concrete  in  (a). 


38 


PILING 


§39 


Concrete  piles  may  also  be  used  in  unreliable  ground,  such 
as  that  made  up  of  ashes  and  the  usual  refuse  used  to  fill  up 
city  lots;  in  fact,  they  can  be  used  to  advantage  wherever  it 
is  necessary  to  carry  the  load  of  a  building  or  a  structure  to 
foundations  firmer  than  can  be  obtained  from  the  upper  strata 
of  the  soil. 


/jlpmumw 


Fig.  29 


56.  Capping  of  Concrete  Piles. — It  is  the  custom  to 
cap  concrete  piles  with  a  concrete  capping  or  a  footing  course. 
In  order  to  form  the  concrete  capping,  the  earth  is  excavated 
from  around  the  top  of  the  piles,  and  a  cinder  or  other  cheap 
concrete  is  then  put  around  them  and  made  level  with  the 
top;  above  this  is  constructed  a  footing  course  of  broken- 
stone  concrete  from  2  to  4  feet  in  thickness.  In  Fig.  29  is 


§39 


PILING 


39 


shown  a  series  of  concrete  piles  driven  in  parallel  rows,  with 
the  trenches  excavated  for  filling  with  cinder  concrete. 

Where  the  thickness  of  the 

capping  is  limited  by  the 

conditions  of  the  foundation, 

the  capping  may  be  made 

shallow — 1  or  2  feet  in  thick- 
• 

ness — and  reinforced  with 
woven-wire  mesh  or  expanded 
metal,  as  shown  in  Fig.  30. 

The  reinforcement  of  the  foot¬ 
ing  in  this  manner  gives  it 
sufficient  strength  to  distrib¬ 
ute  the  weight  between  the 
tops  of  the  several  adjacent 
piles. 

In  the  capping  of  piles,  a 
considerable  saving  is  effected 
by  the  use  of  concrete  piles 


■m# 

mm 

-r7.<T<d-'d-VT 

mxi-V-Yv.r, 

'a&ry&.wg 

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•”(p'  •  *' 

.•*!***  • 

:*•£=» 

mm 

MIS 

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■V 


:0.: 


Fig.  30 

instead  of  wooden  piles.  In 
Fig.  31  (a)  is  illustrated  a  footing  designed  to  be  supported  on 


timber  piles,  and  in  ( b )  is  shown  the  same  footing  designed 
for  concrete  piles.  It  will  be  observed  that  owing  to  the 


40 


PILING 


§39 


greater  number  of  timber  piles  required,  the  concrete  footings 
must  be  extended  to  a  greater  distance  beyond  the  wall. 


Sections  on  the  lines  A  B  and  CD ,  Fig.  31,  are  shown  in 
Fig.  32  at  (a)  and  ( b ),  respectively. 


57.  Placing  of  Concrete  Piles. — In  arranging  con¬ 
crete  piles  under  wall  footings  they  may  be  placed  staggered, 

as  shown  in  Fig.  33 
(a),  or  in  parallel  rows, 
as  shown  in  ( b ).  It 
is  customary  to  stag¬ 
ger  the  piles  if  the 
footing  is  narrow,  and 
to  place  them  in  par¬ 
allel  rows  if  the  foot- 


'  '\ 

'  1 

n 

/  \ 

n 

O' 

(a) 

(  \ 

!  \ 

/  ~N 
/  ' 

\  / 
v  _  ^ 

S~''\ 

1  1 

V  / 

— — 

j  (b) 

Fig.  33 

ing  is  of  a  considerable  width.  Under 
piers,  concrete  piles  may  be  arranged 
in  any  suitable  manner,  it  being  advis¬ 
able  to  place  the  piles  so  that  each  pile 
will  support  the  same  percentage  of 
the  load. 

Generally,  lG-inch  concrete  piles 
should  not  be  driven  closer  together  than  3  feet  from  center  to 
center,  although,  if  occasion  demands,  such  piles  may  be  driven 
as  close  as  30  inches  from  center  to  center.  It  is  frequently 


i-f&R 

f  J 

Fig.  34 


§39 


PILING 


41 


necessary  to  place  piles  as  close  to  an  adjacent  wall  as  the  pile 
driver  will  permit,  which  is  about  30  inches.  Under  light-wall 
piers,  it  is  frequently  found  that  three  piles  will  support  the 
calculated  load.  When  this  is  the  case,  they  may  be  placed 
in  a  triangular  arrangement,  as  shown  in  Fig.  34.  It  is  never 
well  to  place  concrete  piles  in  a  single  row,  as  there  is  a  tend¬ 
ency  for  the  wall  or  footing  constructed  upon  such  piles  to 
tip,  because  the  center  of  the  pile  may  not  be  coincident  with 
the  center  of  the  weight  of  the  wall  and  its  floor  loads.  In 

isolated  pier  or  column  con¬ 
struction,  at  least  four  con¬ 
crete  piles  should  be  used. 
These  piles  should  be  arranged 
as  shown  in  Fig.  35,  as  this  is 


l/ne  of Baseme/y/ f/aor 


c;;-; 


Fig.  35 


Fig.  36 


the  simplest  arrangement  that  will  make  a  secure  bearing  for 
the  pier. 

In  buildings  of  light  construction  and  of  considerable  area, 
a  saving  can  sometimes  be  made  in  the  construction  of  the 
foundations  by  using  a  single  concrete  pile  under  a  column, 
as  shown  in  Fig.  3G.  Such  a  pile  should  be  of  large  size  in 
order  to  give  full  bearing  to  the  column  supported  by  it. 
This  construction  is  admirably  adapted  for  buildings  that 
are  to  be  built  on  made  ground  and  in  cases  where  spread 
footings  of  the  required  size  are  found  too  costly. 

211—31 


42 


PILING 


§39 


CONSTRUCTION  AND  DRIVING  OF  CONCRETE 

PIEES 


RAYMOND  CONCRETE  PILES 

58.  Method  of  Driving  by  Hammer. — The  Raymond 
system  of  concrete-pile  construction  consists  pri¬ 
marily  in  driving  a  tapered  pile  by  using  a  collapsible  driving 
form.  Before  being  driven,  this  form  is  enclosed  in  a  sheet 
steel  casing,  and,  when  driven,  it  is  collapsed  and  withdrawn, 
leaving  the  casing  in  the  ground.  This  casing  is  afterwards 
filled  with  concrete. 

To  illustrate  the  method  of  Raymond  concrete-pile  con¬ 
struction,  reference  is  made  to  Fig.  37.  The  collapsible  steel 
driving  form  is  shown  at  a.  The  shell  of  this  form  is  made 
in  three  sections,  as  shown  in  the  plan  of  the  figure,  and  con¬ 
sists  of  plates  f  inch  in  thickness.  These  sections  are  secured 
to  wedge-shaped  castings  d.  By  means  of  the  pin-connected 
links  c}  the  steel  shell  is  secured  to  the  interior  stem  of  the 
core  e.  This  core  also  carries  cast-steel  collars  /,  which  engage 
with  the  wedge-shaped  castings  d  secured  to  the  sectional 
shell.  When  this  form  is  ready  for  driving,  the  sectional 
shell  is  in  its  extreme  position  of  extension,  and  is  held  there 
by  means  of  the  wedging  device  g.  Upon  the  driving  form 
is  then  placed  the  sheet-steel  casing  h,  made  in  sections,  of 
about  No.  10  gauge  sheet  iron  or  tank  steel.  The  form  carry¬ 
ing  the  tank-steel  casing  is  then  driven  by  means  of  a  steam 
hammer  i.  In  order  to  save  the  top  of  the  driving  form,  there 
is  provided  a  cast-steel  head  j  that  carries  a  wooden  cap  block 
to  receive  the  blow  of  the  hammer.  To  prevent  the  form 
from  collapsing  in  driving,  the  keys  or  wedging  devices  g  are 
used  to  hold  the  stem  d  in  position.  When  the  form  with  its 
sheet-steel  casing  is  driven  to  the  required  depth,  the  wedges, 
or  keys,  are  removed  and  the  stem  released,  thus  collapsing 
the  driving  form  as  shown  in  Fig.  38,  in  which  the  reference 
letters  indicate  corresponding  parts  to  those  similarly  marked 
in  Fig.  37.  The  driving  form  is  then  withdrawn,  leaving  in 


43 


Fig.  38 


44 


PILING 


§39 


the  ground  a  steel-lined  hole,  which  is  filled  with  concrete  and 
tamped  while  being  filled. 

The  advantage  claimed  for  this  system  of  pile  construction 
is  that  it  is  impossible  for  a  soft  stratum  of  earth  to  flow  into 
the  form  of  the  pile  during  construction.  In  constructing  these 
piles,  the  necessary  equipment  consists  of  the  wooden  guides,  a 


steam  pile  driver,  the  driving  core,  and  a  heavy  cornice  brake 
for  bending  the  sheet  iron  used  for  the  casing.  Shears  and 
other  tools  required  for  working  the  sheet  iron  are  also  required. 


59.  Method  of  Driving  by  Water  Jet. —  The  Ray¬ 
mond  concrete  pile  may  also  be  sunk  by  using  the  water  jet. 
This  method  of  forming  and  sinking  these  piles  is  illustrated 
in  Fig.  39.  In  (a)  is  shown  a  nest  of  tapering  sheet-iron  shells. 


§39 


PILING 


45 


To  the  inner  and  smallest  shell  a  cast-iron  end,  or  point,  is 
fastened,  to  which  a  2^ -inch  pipe  with  a  -f-inch  nozzle  is 
attached.  Through  this  pipe  water  is  forced  with  a  pressure 
sufficient  to  scour  out  the  sand  and 
earth,  allowing  the  shell  to  settle. 

When  the  top  of  the  first  shell 
has  reached  the  ground  level  and 
has  come  into  contact  with  the 
next  shell,  it  is  filled  with  concrete. 

As  the  shells  are  tapered,  they  are 
carried  down  one  after  the  other, 
as  shown  in  (6),  (c),  and  ( d ),  each 


•  S 

LA 


'■'■O/. 


•  0::  :• 


•  SS'.WS Sfi 

AA 

HI  m 


o.\ 


*’o'v 


v-:-. 

•  .  .  A',;!','*’;.. 


being  filled  with  concrete  as  the  lyA 
operation  proceeds.  The  2§-inch 
pipe  remains  in  the  center  of  the  AA 
pile,  increasing  the  lateral  strength 
of  the  pile  to  a  considerable  extent. 

The  pile  may  also  be  additionally 
reinforced  by  inserting  rods  near 
the  outer  surface  of  the  concrete. 

This  method  of  construction  may 
be  used  for  piles  as  large  as  2  feet 
in  diameter  at  the  bottom  and  4 
feet  at  the  top.  They  may  be  put 
in  place  through  any  depth  of 
water,  and  to  a  considerable  pene¬ 
tration  of  sand  or  silt.  This  sys¬ 
tem  is  used  only  in  penetrating  (a) 

quicksand,  or  soft  material,  or  such 
soils  as  will  scour,  or  flow  out,  from  under  the  point  of  the 
pile  when  water  is  forced  through  the  jet  pipe.  The  pipe  is 
strengthened  at  every  section  by  a  brace  extending  to  the 
sides,  as  shown. 

This  system  of  pile  construction  has  been  tested  in  the 
Missouri  River,  near  Omaha,  Nebraska,  where  a  pile  10  inches 
in  diameter  at  the  bottom  and  20  inches  at  the  top  was  sunk 
to  the  depth  of  75  feet  in  sand,  with  pressure  of  water  of  about 
40  pounds. 


Fig.  40 


(b) 


40 


PILING 


§39 


SIMPLEX  CONCRETE  PILES 

60.  Standard  Simplex  Concrete  Piles. — The  Sim¬ 
plex  concrete  pile  of  standard  construction  is  formed 
in  the  soil  by  either  of  the  two  methods  illustrated  in 
Figs.  40  and  42.  The  first  method,  shown  in  Fig.  40  (a), 
consists  in  driving  into  the  soil  the  heavy  steel  cylinder,  or 


Fig.  41 


form,  a,  which  is  provided  at  the  bottom  with  a  cast-iron 
point,  or  driving  shoe,  b.  This  form,  the  upper  end  of  which 
is  open,  is  driven  through  the  soft  soil  to  the  gravel  or  hard  pan, 
after  which  it  is  entirely  filled  with  plastic  concrete.  The 
steel  form  is  then  withdrawn,  as  shown  in  the  figure  at  (a), 


§39 


PILING 


47 


leaving  the  iron  shoe  in  position.  In  this  manner  the  con¬ 
crete  fills  the  entire  void  left  by  the  form,  cementing  and 
uniting  with  the  surrounding  soil.  When  the  form  has  been 
entirely  withdrawn,  the  concrete  pile  is  allowed  to  set,  after 
which  it  is  ready  to  receive  the  cappings,  or  footings,  of  the 
foundations  that  the  piles  are  designed  to  support.  The  form 
of  the  concrete  pile  with  the  cast- 
iron  shoe  in  place  is  shown  in 
Fig.  40  (b). 

In  order  to  show  more  clearly 
the  use  of  the  cast-iron  pointed 
shoe  and  the  method  of  driving 
the  steel  tube  and  driving  form, 
attention  is  directed  to  Fig.  41. 

The  steel  driving  form  is  here 
shown  in  position  between  the 
guides  of  the  hammer  and  directly 
over  the  cast-iron  pointed  shoe, 
which  has  been  placed  in  the 
position  required  for  the  pile. 

These  pointed  shoes,  besides  assist¬ 
ing  in  the  penetration  of  the  soil, 
prevent  the  earth  from  filling  the 
tube.  They  are  also  very  conve¬ 
nient  in  placing  or  locating  the  piles, 
as  they  may  be  readily  placed  as 
required  by  the  plans  and  the 
driving  machine  may  be  set  so 
that  the  tube,  or  form,  will  be 
directly  over  them. 

,  J  Fig.  42 

/ 

61.  The  second  method  of  constructing  the  standard 
Simplex  concrete  pile  is  shown  in  Fig.  42.  The  hollow  steel 
form  or  cylinder  a,  view  (a),  instead  of  being  provided  with 
a  cast-iron  shoe,  as  in  the  preceding  case,  is  furnished  with 
hinged  jaws  as  at  b,  a  detail  of  which  is  shown  in  Fig.  43. 
These  jaws  are  closed  while  driving,  and  yet  will  open  to  the 
full  diameter  of  the  pipe,  or  tube,  when  being  pulled,  or  drawn, 


48 


PILING 


§39 


to  let  the  concrete  pass  out.  When  this  form  has  been  driven 
to  the  required  depth,  it  is  filled  with  concrete  and  withdrawn, 
allowing  the  jaws  to  open  and  deposit  the  concrete.  By  this 
method,  the  expense  of  a  cast-iron  shoe  is  avoided.  The 
finished  concrete  pile  is  shown  in  Fig.  42  ( b ). 

By  the  Simplex  system  of  construction  there  results  a 
cylindrical  concrete  pile,  every  particle  of  which  has  been 


Fig.  43 


Fig.  44 


forced  into  the  hole  under  pressure,  conforming  itself  to  all 
the  roughnesses  of  the  hole  and  cementing  itself  to  the  sides. 
The  Simplex  pile  has  great  side  friction  and  large  end  bearing, 
the  diameter  down  in  the  hard  pan  being  16  inches. 


(>2.  Simplex  Molded  Concrete  Pile. — The  Simplex 
system  of  pile  construction  also  embodies  the  use  of  a  molded 


§39 


PILING 


49 


concrete  pile.  Molded  concrete  piles  arc  generally  driven 
with  a  hammer,  in  the  same  manner  as  wooden  piles,  with  the 
exception  that  a  buffer  is  used  under  the  hammer  to  lessen  the 
shock;  however,  where  the  soil  will  permit,  they  are  driven 


Fig.  45 


with  a  water  jet.  The  objection  to  the  first  method  is  that 
the  concrete  pile  is  liable  to  crack  badly  or  become  otherwise 
injured;  the  latter  method  can  be  used  only  in  soils  favorable 
to  this  process. 


50 


PILING 


§39 


The  Simplex  molded  piles  and  the  method  employed  to 
drive  them  overcome  these  difficulties  by  the  method  of  con¬ 
struction  illustrated  in  Fig.  44.  In  this  method  the  driving 
shell  a,  view  (a),  shod  with  the  hinged-jaw  device,  is  driven 
to  the  required  depth  until  a  solid  bearing  is  reached,  when 
several  buckets  of  concrete  are  dumped  into  the  driving  form, 
or  shell,  and  the  form  partly  withdrawn,  the  concrete  being 
well  rammed.  When  this  is  accomplished,  several  buckets  of 

soft  grout  are  poured  in  the  form 
and  the  previously  molded  pile  is 
lowered  into  place.  The  driving 
form  is  then  slowly  withdrawn,  and 
the  concrete  pile  with  the  cement 
grout  fills  the  space  formerly  occu¬ 
pied  by  the  driving  shell,  or  form. 
The  finished  pile  in  place  is  shown 
in  view  ( b ) .  These  Simplex  piles  are 
molded  on  end,  in  the  manner  illus¬ 
trated  in  Fig.  45,  and  may  be  rein¬ 
forced  in  any  desirable  manner. 
The  figure  shows  the  derrick  and 
bucket  used  to  hoist  the  concrete, 
which  is  mixed  on  the  ground,  to 
the  top  of  the  platform. 


■\d. 


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vo-;-.'- 


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1 


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.  ' 

M : 

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m. 

: 

m  ■ 


;&.■ 


i  ■ 
4  •: 


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G3.  Simplex  Sliell,  or  Wharf, 
Pile. — There  is  another  Simplex 
concrete-pile  construction  known  as 
the  sliell,  or  wliarf,  pile;  it  is 
used  in  very  soft  soil  or  in  water. 
The  method  of  driving,  as  well  as 
the  form  of  this  pile,  is  shown  in 
Fig.  46  (a)  and  ( b ).  As  in  the  prece¬ 
ding  case,  the  driving,  or  form,  shell  is  driven  to  the  required 
depth  and  soft  concrete  is  deposited  in  the  bottom,  forming  a 
layer,  as  shown  at  a.  Then  the  form  is  partly  withdrawn  and 
inside  it  is  placed  a  steel  cylindrical  shell  that  rests  on  the  con¬ 
crete  at  the  bottom.  The  shell  is  then  filled  with  concrete  and 


(b) 


Fig.  46 


§39 


PILING 


51 


the  driving  form  withdrawn.  In  this  manner,  the  steel  shell 
protects  the  concrete  until  it  has  set.  The  shell  cannot 
codapse  from  the  pressure  of  the  soft  soil  on  account  of  the 
concrete  filling  it,  nor  will  the  cement  be  washed  from  the 
concrete  forming  the  filling  of  the  shell  or  the  pile. 

This  pile  is  admirably  adapted  to  the  construction  of  wharf 
foundations  and  for  the  support  of  the  footings  of  buildings 
where  it  is  necessary  to  penetrate  a  soft  mud  or  quicksand. 
Piles  as  large  as  36  inches  in  diameter  may  be  formed  in  this 
manner,  and  when  properly  reinforced  they  will  sustain 
thousands  of  pounds. 


COMPOSITE  PILES 

64.  A  composite  pile  consists  of  a  wooden  pile  on 
the  top  of  which  is  constructed  a  concrete  pile,  the  wooden 
pile  being  driven  to  such  a  depth  as  to  allow  its  top  to  be 
below  the  permanent  water-line.  Piles  of  this  kind  may  be 
used  to  advantage  when  it  is  necessary  to  drive  piles  to  a 
depth  of  70  to  100  feet.  Ordinarily,  with  wooden  piles,  it  is 
necessary  to  excavate  down  to  the  permanent  water-line, 
so  that  the  pile  may  be  sawed  off  and  the  concrete  pier  or 
footing  be  completed  up  from  this  point.  It  is  not  unusual 
in  instances  of  this  kind  to  excavate  15  or  20  feet,  which 
operation  is  ordinarily  an  expensive  one.  The  use  of 
composite  piles  overcomes  this  difficulty;  besides,  they  are 
cheaper  than  the  all-concrete  pile,  and  ordinarily  can  be  used 
at  less  cost  than  by  using  all  wooden  piles,  cutting  them  off 
below  permanent  water-line,  and  completing  the  concrete  or 
masonry  piers  from  this  point  to  the  ground  level. 

65.  The  method  of  constructing  composite  piles  is  illus¬ 
trated  in  Fig.  47.  In  (a)  is  shown  the  first  part  of  the  oper¬ 
ation.  The  wooden  pile  is  driven  until  its  top  is  near  the 
ground  line,  the  head  of  the  pile  being  protected  from  splinter¬ 
ing,  or  brooming,  by  the  cast-steel  pile  cap  a  and  the  cast-steel 
driving  head  b.  The  driving  head  contains  a  wooden  block  c 
that  takes  up  the  shock  of  the  hammer,  and  by  this  means 
the  top  of  the  pile  is  preserved.  In  order  to  drive  the  wooden 


Fig.  47 


52 


§39 


PILING 


53 


pile  to  its  final  position,  with  its  top  well  below  the  permanent 
water-line,  the  follower  and  driving  form  d,  Fig.  47  ( b ),  is 
used.  As  will  be  observed,  both  the  follower  and  the  driving 
form  consist  of  double  extra-heavy  pipe,  which  is  placed  on 
the  top  of  the  wooden  pile.  This  pipe  is  centered  by  the 
iron  dowel-pin  and  casting  /,  which  replaces  the  cap  shown 
in  (a),  and  is  fitted  with  a  driving  head  b.  Both  the  form 
and  the  follower  are  driven  together,  forcing  the  wooden  pile 
to  its  final  position.  The  driving  form,  which  is  reinforced 
at  the  lower  efid,  is  provided  with  a  cast-iron  ring  h,  and  this 
is  left  in  position  with  the  completed  pile,  as  shown  in  (c). 
When  the  wooden  pile  has  been  driven  to  the  proper  depth, 
the  follower  is  removed  and  the  concrete  is  dumped  into  the 
driving  form,  which  is  then  withdrawn,  forming  the  concrete 
pile  extension,  as  shown  at  i,  Fig.  47  (c). 

It  will  be  noticed  that  the  junction  between  the  concrete 
pile  extension  and  the  wooden  pile  has  considerable  lateral 
strength  on  account  of  the  cast-iron  ring  and  the  dowel-pin. 
The  ring  greatly  reinforces  the  end  of  the  concrete  pile,  and 
the  dowel-pin  prevents  lateral  displacement. 

66.  One  of  the  advantages  of  using  the  composite  pile  is 
that  a  short  pile  driver  may  be  employed.  This  is  important 
where  piles  70  feet  or  more  in  length  are  to  be  driven.  The 
concrete  portion  of  the  pile  may  be  provided  with  any  neces¬ 
sary  reinforcement  and  may  be  used  for  anchorage.  It  is 
claimed  for  the  composite  piles  that  they  are  excellent  in 
wharf  construction,  as  the  marine  w’ood  borers  will  not 
attack  wooden  piles  below  the  river  bottom.  The  concrete 
extension  in  wharf  work  should  be  placed  by  using  an  iron 
shell,  as  described  in  conjunction  with  the  shell,  or  wharf, 
concrete  pile. 

HAMMER-  OR  JET-DRIVEN  CONCRETE  PILES 

67.  Corrugated  Piles. — The  concrete  pile  shown  in 
section  in  Fig.  48  is  known  as  the  corrugated  concrete  pile. 
It  is  the  invention  of  Frank  B.  Gilbreth,  and  is  made  and 
molded  in  wooden  forms.  When  the  concrete  has  set  suf- 


I 


54 


PILING 


§39 


ficiently,  the  pile  is  driven  with  a  water  jet  and  steam  pile 
driver.  As  shown  in  the  section,  the  pile  is  molded  octagonal 

in  form,  with  fluted  sides,  and  is 
cast  with  a  hole  through  the  center 
to  facilitate  the  use  of  the  water 
jet  in  driving.  The  octagonal 
shape  is  used  in  order  to  cheapen 
the  cost  of  the  form  work  and  the 
flutes  are  used  to  increase  the  sur¬ 
face  and  consequently  the  fric¬ 
tional  resistance  of  the  pile  against 
settling.  The  pile  is  reinforced, 
in  order  to  strengthen  it  for 
handling  and  driving.  The  reinforcement  consists  of  Clinton 
electrically  welded  wire  fabric,  the  rods  running  lengthwise 
of  the  pile  being  |  inch  in  diameter,  and  the  rods  extending 
around  the  pile  ■§•  inch.  The  longitudinal,  or  vertical,  rods 
are  placed  about  3  inches  from  center  to  center,  and  the 
J-inch  rods,  or  wires, 
are  12  inches  on 
centers.  The  hole 
through  the  center  of 
the  pile  is  about 
inches  in  diameter, 
and  is  molded  by 
using  a  tapering  plug, 
which  can  readily  be 
withdrawn. 


68.  In  driving 
this  type  of  pile,  an 
ordinary  pile  driver 
is  used,  the  force  of 
the  blow  being  re¬ 
lieve  d  by  a  cap. 

This  cap,  which  is 
about  3  feet  in  height,  fits  over  the  head  of  the  pile  and 
forms  a  cushion  for  the  blows  of  the  driving  hammer. 


4 


rn 


d 


a 


:.:3x 

r-Pr- 


TJ 


Fig.  49 


Fig.  48 


5  39 


PILING 


55 


Fig.  50 


The  cap  is  constructed  as  shown  in  Fig.  49. 
In  this  figure,  at  a,  is  shown  a  steel  shell  of  a 
diameter  sufficient  to  fit  over  the  head  of  the 
concrete  pile.  This  shell  is  slotted  at  one 
side,  so  as  to  allow  the  pipe  used  for  the  water 
jet  to  enter  and  pass  down  through  the  hole 
in  the  pile.  Directly  on  the  top  of  the  con¬ 
crete  pile  a  plug  of  wood  b  is  placed.  Several 
layers  consisting  of  pieces  of  hose  or  rope  f 
are  inserted  between  this  plug  and  a  wooden 
plunger  c.  This  plunger  is  provided  with  a 
cast-iron  cap  d,  and  this  cap  is  fitted  with 
the  wooden  plug  e,  to  prevent  it  from  being 
directly  hit  by  the  hammer.  The  steel  shell 
is  provided  with  channel-iron  guides  on  each 
side.  Ordinarily,  the  pile,  after  8  days,  has 
been  found  to  be  set  sufficiently  to  allow 
driving.  In  sinking  a  pile,  the  water  jet  is 
used  in  conjunction  with  the  hammer.  This 
jet  consists  of  a  1^-inch  pipe  connected  up 
to  a  high-pressure  pump  and  passing  down 
through  the  hole  in  the  pile.  The  water  jet 
loosens  up  the  gravel  and  earth  and  carries 
them  up  the  corrugations  on  the  outside  of 
the  pile,  these  corrugations  acting  as  an  ex¬ 
haust  to  the  jet. 

One  of  these  piles  successfully  withstood 
the  blows  of  a  2,500-pound  hammer  falling 
25  feet,  and  striking  from  20  to  30  blows. 
In  some  instances,  piles  of  this  kind  have  been 
put  in  place  within  2  minutes  after  the  dri¬ 
ving  has  been  started. 

Fig.  50  shows  a  molded  concrete  pile  of 
octagonal  section  with  two  grooves  or  corru¬ 
gations  on  each  side  of  the  octagon.  This 
figure  also  shows  clearly  the  reinforcement 
of  the  pile.  The  hole  down  which  the  water 
pipe  passes  is  also  clearly  shown. 


5G 


PILING 


§39 


Fig.  51 


69.  Clienoweth  Steel -Concrete  Pile. —  The  Clien- 
owetli  steel-concrete  pile  is  made  by  winding  a  woven- 
wire  cloth  with  a  layer  of  concrete  of  plastic  consistency 
and  molding  -  the  same  to  form  a  reinforced-concrete  pile. 

A  section  of  a  finished  pile  is  shown  in 
Fig.  51,  which  illustrates  the  method  of 
winding  the  wire  webbing  with  the  con¬ 
crete  to  form  the  pile.  As  will  be  noticed, 
the  wire  cloth,  starting  from  the  steel  rod 
at  the  center,  takes  the  form  of  a  volute, 
or  spiral,  with  the  center  of  the  volutions 
at  the  center  of  the  pile.  The  piles  are 
made  by  a  special  machine,  which  rolls  the  concrete  and  the 
wire  cloth,  or  webbing,  together. 

These  piles  may  be  made  from  12  to  1G  inches  in  diameter, 
and  as  long  as  30  to  40  feet.  The  average  pile  is  12  inches  in 
diameter  and  30  feet  long,  and  is  reinforced  at  the  center  with 
a  steel  winding  rod  1  inch  square  and  about  150  square  feet 
of  wire  cloth,  or  webbing,  made  of 
wires  of  No.  17  Brown  &  Sharpe 
gauge,  woven  with  lj-inch  mesh. 

The  Chenoweth  piles,  when  the 
concrete  has  set,  have  considerable 
transverse  and  compressive  stress  and 
are  driven  with  the  ordinary  pile 
driver,  having  a  sand  cushion  or  other 
cushioned  cap  in  order  to  protect  the 
top.  Where  it  is  desirable  to  drive 
these  piles  by  a  water-jet  process,  a 
pipe  may  be  substituted  for  the  cen¬ 
tral  winding  rod. 

The  usual  cushion  cap  used  for  dri¬ 
ving  these  piles  is  shown  in  Fig.  52. 

As  shown,  a  cast-iron  cap,  or  casing  a,  fig.  52 

fits  over  the  top  of  the  concrete  pile.  Frequently,  a  wooden 
block  b  is  placed  over  the  top  of  the  pile  and  on  the  top  of  this 
is  filled  a  layer  of  sand  covered  by  a  wooden  driving  plug  cy 
which  fits  into  the  upper  end  of  the  iron  casing.  This  plug  is 


§39 


PILING 


57 


protected  by  a  welded  wrought-iron  ring  to  prevent  brooming. 
The  finished  Chenoweth  concrete  pile  is  shown  in  Fig.  53  (a), 
and  the  usual  steel  webbing  used 
for  the  reinforcement  in  the  flat  is 
shown  in  ( b ). 


Bv 


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if. ; 


.VvWSr-’: 

;  i 


p  # 

>-•.  ■  f. 

•. 

•ijl  '  - 

rv-# 

I  *  tm  . 

|;ap 

i;K=li 
•  •  - 


SPECIAL  SYSTEM  OF  CONCRETE 

FOUNDATION  CONSTRUCTION 

70.  A  type  of  concrete  foun¬ 
dation  construction  that  has  been 
somewhat  extensively  used  in 
France,  and  which  is  being  intro¬ 
duced  into  the  United  States,  is 
known  as  the  Compressol  sys¬ 
tem  of  concrete-pier  construc¬ 
tion.  While  this  system  is  not 
known  as  concrete-pile  construc¬ 
tion,  yet  it  is  very  similar.  The 
distinguishing  feature  of  the  Com¬ 
pressol  system  consists  in  driving  a 
hole  into  the  ground  by  repeatedly 
dropping  a  heavy  pointed  weight, 
and  then  filling  the  hole  so  formed 
with  concrete.  Fig.  54  shows  the 
device  used  to  penetrate  the  soil. 

At  a  is  shown  the  derrick,  or  dri¬ 
ving  machine,  which  is  somewhat 
similar  in  construction  to  the  timber 
work  of  the  ordinary  pile  driver, 
and  at  b  is  illustrated  the  pointed 
driving  weight  hoisted  to  position 
and  ready  to  drop.  This  weight 
when  repeatedly  dropped  pene¬ 
trates  the  soil  in  the  manner 

shown  in  Fig.  56.  When  the  required  depth  of  pene¬ 
tration  has  been  reached,  the  hole  is  filled  with  concrete, 
each  lot  being  tamped  by  dropping  a  weight  of  the  shape 

211—32 


n>) 


Fig.  53 


58 


PILING 


§39 


shown  in  Fig.  55.  The  concrete  is  compacted  and  forced  out 
by  this  process,  so  that  the  hole  is  spread  into  the  shape 
shown  in  Fig.  57  by  the  concrete  forced  into  it.  By  this 

means  is 
formed  a 
solid  con¬ 
crete  pier  of 
a  more  or 

less  cylindrical  section  and 
a  spread  base.  Such  con¬ 
crete  piers  have  been 
known  to  support  with 
safety  as  much  as  90  tons. 

One  of  the  advantages 
claimed  for  the  Compressol 
system  is  that  the  falling 
Fig.  54  weight  compresses  the  soil 

around  the  edges  of  the  hole  and  prevents  water  from  pene- 


Fig.  55 


Fig.  56 


■■ 

:.WsF$%A 


sm&r# 


k'.e  ^ 


trating.  Should  the  compression  of  the  soil  not  be  sufficient 
to  do  this,  a  quantity  of  clay  or  puddle  can  be  placed 


§30 


PILING 


59 


in  the  hole,  and  the  blows  of  the  weight  will  force  it  out, 
lining  the  opening  and  forming  a  jacket  sufficiently  waterproof 
to  keep  the  hole  dry  while  the  concrete  is  being  placed  and 
tamped. 


COST  OF  CONCRETE  PIEES 

71.  Comparative  Cost  of  Concrete  and  Wooden 
Piles. —  Although  concrete  piles  cost  several  times  as  much 
per  linear  foot  as  wooden  piles,  there  is  frequently  a  con¬ 
siderable  saving  made  by  using  them,  not  only  because 
fewer  are  needed  to  carry  the  same  total  load,  but  also  because 
the  amount  of  the  foundation  masonry  and  excavation  is 
materially  reduced.  One  of  the  largest  items  of  cost  involved 
in  the  use  of  wooden-pile  foundations  is  the  depth  of  the 
masonry  foundation  required  to  permit  the  tops  of  the 
wooden  piles  to  be  located  below  the  permanent  water-line, 
whereas,  concrete  piles  may  extend  any  distance  above  the 
water-line,  and  therefore  require  only  a  capping  of  concrete 
or  masonry. 

The  cost  of  wooden  piles  ranges  from  25  to  50  cents 
per  linear  foot,  depending  on  the  availability  of  the  timber  and 
the  conditions  encountered  in  driving.  The  cost  of  concrete 
piles,  driven,  ranges  from  90  cents  to  $1.50  per  linear  foot. 

72.  In  the  construction  of  the  new  United  States  Naval 
Academy,  it  was  found  more  economical  to  use  concrete  piles 
than  to  employ  timber  piles;  also,  in  place  of  2,193  wooden 
piles  8S5  concrete  piles  were  found  to  answer  the  same  pur¬ 
pose.  By  using  the  concrete  piles  3,504  cubic  yards  of  exca¬ 
vation  was  saved,  and  the  estimated  3,250  cubic  yards  of  con¬ 
crete  footings  required  for  the  timber  piles  was  reduced  to 
986  cubic  yards.  Besides,  it  was  estimated  that  the  shoring 
and  pumping  incidental  to  making  the  necessary  excavations 
for  the  wooden-pile  construction  and  the  cutting  off  of  the 
timber  piles  would  cost  $4,000. 

A  comparison  of  the  estimated  cost  of  wooden  and  concrete 
piles  is  as  follows: 


60 


PILING 


§39 


Wooden  Piles 

2,193 . at  $9.50  $20,833.50 

4,542  cubic  yards  excavation  at  .40  1,816.80 

3,250  cubic  yards  concrete  .  .at  8.00  26,000.00 

5,222  pounds  I  beams . at  .04  208.88 

Shoring  and  pumping .  4,000.00 

Total  cost  .  $52,859.18 


Concrete  Piles 

855  piles . at  $20.00  $17,100.00 

1,038  cubic  yards  excavation  at  .40  415.20 

986  cubic  yards  concrete  .  .  .at  8.00  7,888.00 

Shoring  and  pumping .  0,000.00 


Total  cost .  $25,403.20 

Difference  in  cost .  $27,455.98 


From  this  comparison  it  is  observed  that  the  estimated 
saving  is  more  than  $27,000. 

Although  it  is  true  that  these  comparative  figures,  so  far 
as  the  cost  of  the  wooden  piles  is  concerned,  are  based  on 
assumptions,  it  is  nevertheless  certain  that  since  these  assump¬ 
tions  were  made  on  the  average  of  the  existing  conditions, 
they  were  nearly  correct,  and  the  conclusion  was  that  in  this 
instance  the  use  of  timber  piles  would  be  attended  with  a 
great  increase  in  cost  of  the  foundation  construction.  In 
other  localities  and  with  other  conditions,  it  is  probable  that 
the  difference  between  the  cost  of  the  timber  and  concrete 
piles  would  not  be  so  marked.  There  are  so  many  factors 
entering  into  the  cost  of  both  kinds  of  piles  for  any  particular 
locality  that  in  designing  foundations  of  this  kind  it  is  best, 
where  cost  is  important,  to  obtain  prices  for  both  timber 
and  concrete-pile  construction. 


73.  Cost  of  Concrete  Piles  and  Price  Quota¬ 
tions. — Generally,  in  establishing  the  price  for  concrete 
piles,  an  average  depth  of  pile  is  used  for  the  basis  of  the  unit 
prices  per  foot,  and  a  minimum  number  of  feet  to  be  driven 
is  also  stipulated  in  the  contract.  The  price  is  also  fixed 


§39 


PILING 


61 


per  foot  for  piles  longer  than  the  average  length,  and  the 
•  reduction  in  price  per  foot  is  made  for  piles  shorter  than  the 
average  length.  For  instance,  assume  that  bids  are  asked 
on  100  concrete  piles,  driven  to  an  average  depth  of,  say, 
20  feet,  but  that  owing  to  the  nature  of  the  soil  and  the  design 
of  the  foundation,  some  of  the  piles  will  be  shorter  than  20  feet 
and  some  much  longer.  The  cost  quotations  for  concrete- 
pile  work  of  this  character  will  probably  stipulate  that 
100  piles  at  an  average  depth  of  20  feet,  with  a  minimum 
total  of  2,000  feet,  will  be  driven  for  say  $1.35  per  linear  foot, 
or  $2,700;  and  that  for  piles  longer  than  20  feet  the  extra  price 
per  foot  will  be  $1,  and  the  deduction  for  piles  of  shorter 
length  than  20  feet  will  be  80  cents  per  foot.  The  reason  for 
so  arranging  the  prices  is  on  account  of  the  labor  involved 
in  moving  the  driving  machine  for  the  short  piles  and  the  cost 
of  getting  it  to  the  site  and  setting  it  up  to  commence  the 
driving.  On  the  other  hand,  the  cost  of  a  long  pile  is  greater 
than  that  of  a  short  one.  It  can  readily  be  seen  that  the 
deduction  for  shorter  piles  cannot,  as  a  rule,  be  so  great  per 
foot  as  the  extra  price  for  piles  longer  than  the  average,  for 
if  the  piles  were  very  short,  the  profit  on  the  money  earned  in 
driving  a  single  pile  would  be  consumed  in  the  labor  involved 
in  moving  and  getting  the  driving  machine  in  position. 

Prices  have  been  quoted  for  the  several  kinds  of  concrete 
piles  that  are  formed  in  the  ground,  ranging  from  $2.25  to 
$1.35  per  linear  foot.  The  former  price  was  high  on  account 
of  the  few  piles  to  be  driven,  and  also  because  of  the  severe 
driving  conditions  that  existed  and  made  the  moving  and 
maneuvering  of  the  driving  machine  difficult.  Prices  that 
have  been  quoted  for  driving  concrete  piles  of  the  Simplex 
and  Raymond  type  are  $1.46  and  $1.40  per  linear  foot,  based 
on  a  total  minimum  of  about  2,000  linear  feet,  and  on  piles 
about  16  inches  in  diameter  and  an  average  length  of  about 
20  feet. 


62 


PILING 


§39 


STRENGTH  AND  REINFORCEMENT  OF  CONCRETE 

PILES 

74.  Strength  of  Concrete  Piles. —  It  is  customary 
to  assume  that  the  bearing  strength  of  properly  constructed 
concrete  piles  is  from  20  to  30  tons  per  pile  for  piles  of  the 
average  size,  which  is  about  16  inches  in  diameter. 

Concrete  piles  are  generally  constructed  of  concrete  com¬ 
posed  of  1  part  of  cement,  2\  parts  of  sand,  and  5  parts  of 
gravel  or  crushed  stone.  As  this  concrete  mixture  is  a  good 
one  and  has  considerable  crushing  resistance,  it  is  well 
within  conservative  practice  to  assume  that  a  16-inch 


Fig.  58 


diameter  concrete  pile  will  sustain  with  safety  a  load  of 
25  tons. 

Bearing  tests  that  have  been  made  on  concrete  piles  have 
been  very  successful,  showing  that  they  will  sustain,  with 
very  little  settlement,  much  more  than  25  or  30  tons  per  pile. 
In  Fig.  58  is  shown  a  test  load  of  300  tons,  supported  on  five 
Simplex  concrete  piles  each  16  inches  in  diameter.  This  test 
was  made  on  a  crane  foundation  for  the  Westinghouse 
Machine  Company,  Pittsburg,  and  no  appreciable  settlement 
was  observed. 


§39 


PILING 


63 


The  Raymond  concrete  pile  has  been  tested  with  equal 
success,  as  piles  22  feet  6  inches  long  driven  in  sand  and  clay 
fill,  with  soft  bottom,  sustained,  under  governmental  test, 
at  the  site  of  the  Annapolis  Naval  Academy,  133,270  pounds, 
making  a  total  load  on  a  single  pile  of  over  66  tons.  The 
result  of  this  test  showed  a  very  slight  settlement,  and  was 
particularly  remarkable  from  the  fact  that  the  pile  did  not 
reach  bed  rock  or  hard  pan. 


o* 

Fig.  59 


A  Gilbreth  molded  pile  of  average  size,  which  is  about 
16  inches  in  diameter,  has  sustained  with  no  appreciable 
settlement  a  total  load  of  45  tons. 

An  important  point  to  observe  in  the  design  of  concrete- 
pile  foundations  is  to  arrange  the  piles  so  that  each  pile  will 
sustain  practically  the  same  load,  and  choice  should  be  made 
of  the  piling  plan  that  most  nearly  accomplishes  this  result. 


64 


PILING 


§39 


For  instance,  a  piling  plan  that  gives  a  variation  of  from 
17  to  22  tons  on  the  piles  would  be  much  better  than  an 
arrangement  in  which  the  piles  were  subjected  to  from  17  to 
26  tons  per  pile.  With  careful  study,  the  piles  can  usually 
be  so  arranged  and  spaced  as  to  approach  uniform  loads 
on  each  pile. 


75.  Reinforcement  of  Concrete  Piles. —  Concrete 
piles  formed  in  the  ground  are  best  reinforced  by  vertical 

rods.  These  rods,  if  required,  may  be  tied 
together  with  wire  ties  as  the  form  is  filled. 

Molded  concrete  piles  may  be  reinforced 
with  either  vertical  rods  or  woven-wire  mesh. 
Concrete  piles  require  reinforcement  only 
when  their  lateral  stiffness  has  to  be  increased, 
as  where  they  are  subjected  to  the  severe  con¬ 
ditions  of  driving  by  the  drop  hammer,  or  in 
wharf  or  other  structures  where  the  piles 
might  be  required  to  resist  a  transverse  stress. 

Concrete  piles  used  for  stack  foundations, 
or  other  high  structures  are  usually  rein¬ 
forced  with  vertical  rods,  the  rods  extending 
above  the  top  of  the  concrete  of  the  pile,  as 
shown  in  Fig.  59.  These  reinforcing  rods 
may  be  bent  over  the  rods  in  the  footings,  in 
order  to  form  an  anchorage,  or  they  may 
extend  into  the  footing  courses  or  into  the 
foundation  itself  when  the  same  is  of 
concrete. 

Concrete  piles,  owing  to  the  facility  with  which  they  may 
be  reinforced,  and  because  of  the  grip  or  bond  that  they  have 
on  the  earth  into  which  they  are  driven,  make  excellent 
anchorage  for  stacks,  water  towers,  stand  pipes,  or  other 
high  structures  that  have  small  bases  and  are  liable  to  over¬ 
turning  moments  from  wind  pressure. 

Sometimes  concrete  piles  are  molded  square  in  section,  when 
they  are  reinforced  with  four  longitudinal  rods  a,  as  shown 
in  Fig.  60.  These  rods  are  cross-tied  with  wire  ties  b.  Such 


Fig.  60 


§39 


PILING 


65 


piles  as  the  one  illustrated  are  designed  to  be  driven  by  means 
of  a  drop  hammer.  Where  it  is  necessary,  they  are  shod  with 
a  sheet-iron  shoe  c.  Such  reinforced-concrete  piles  as  the  one 
illustrated  in  Fig.  60  can  be  driven  close  together,  like  sheet 
piling. 


REINFORCED-CONCRETE  SHEET  PILING 

76.  In  some  instances,  reinforced-concrete  sheet  piling 
has  been  used  where  a  permanent  sheathing  was  required  in 
soft  soil,  or  for  wharf  work.  A  type  of  reinforced-concrete 
sheet  piling  is  illustrated  in 
Fig.  61.  The  reinforced- 
concrete  sheet  piles  shown 
in  view  (a)  are  strengthened 
by  means  of  four  rods  b 
connected  with  wire 
-clamps,  the  latter  being 
cross-tied  by  flat  irons.  A 
projection  e,  Fig.  61  ( b ),  is 
left  near  the  base  of  the 
long  side  of  each  pile  and 
a  semicircular  groove  /  runs 
from  this  projection  to  the 
top.  The  adjacent  side  of 
the  next  pile  is  provided 
with  a  similar  groove,  so 
that,  in  driving,  the  pro¬ 
jection  on  one  pile  slides 
in  the  groove  of  the  last 
one  driven. 

An  iron  pipe  that  fits 
the  grooves  of  two  adjacent 
piles  is  connected  by  means 
of  a  hose  with  a  pump-  or 
a  water  tank.  This  pipe  serves  as  a  guide,  and  the  sand  that 
might  jam  the  grooves  is  forced  out  by  the  water.  After  the 
pile  is  driven,  this  pipe  is  withdrawn  and  a  water-tight  joint 
is  secured  by  filling  the  grooves  with  cement. 


( b ) 


66 


PILING 


§39 


While  driving  the  sheet  piles  illustrated  in  Fig.  61,  the 
head  is  protected  by  a  steel  cap  a  previously  filled  with  sand, 
thus  forming  a  cushion  that  distributes  the  pressure  of  the 
blow  from  the  hammer.  The  head  should  be  of  smaller 
diameter  than  the  body  of  the  pile  so  as  to  allow  a  clearance 
for  the  application  of  the  steel  cap.  By  this  arrangement, 
the  iron  rods  b  may  be  allowed  to  project  above  the  head  so 
that  they  may  be  connected  with  other  parts  of  the  structure. 
The  cap  is  closed  at  the  lower  end  by  a  clay  ring  c  held  by  a 
plug  of  hemp  or  spun  yarn  d. 


STEEL  AND  OTHER  METALS 


IRON  AND  STEEL 


GENERAL  CHARACTERISTICS 

1.  The  materials  largely  used  in  structural  engineering 
are  iron  and  steel.  Iron  may  be  of  two  kinds — cast  iron 
and  wrought  iron.  Cast  iron  can  be  melted  and  pbured 
into  molds,  after  which  it  again  solidifies.  This  process 
is  known  as  casting.  Wrought  iron  can  be  heated  until  it 
becomes  plastic,  when  it  may  be  worked  into  various  shapes, 
either  under  a  hammer  or  in  a  press. 

Steel  is  simply  a  special  form  of  iron,  and  may  be  divided 
into  several  classes,  according  to  the  mode  of  manufacture  or 
the  admixture  of  certain  other  materials. 

In  order  to  become  familiar  with  the  physical  properties 
of  iron  and  steel,  it  is  desirable  to  know  something  of  their 
metallurgy;  that  is,  of  the  process  employed  in  their  manu¬ 
facture.  The  methods  of  producing  iron  and  steel  have 
marked  effects  on  their  qualities,  while  the  presence  of  small 
quantities  of  other  elements,  sometimes  as  impurities,  may 
have  still  greater  effects.  One  element  that  has  a  very 
important  bearing  on  the  properties  of  iron  and  steel  is 
carbon.  Other  substances  affecting  them  in  a  greater  or  less 
degree  are  sulphur,  phosphorus,  tungsten,  nickel,  chromium, 
and  manganese.  Small  percentages  of  some  of  these  ele¬ 
ments  will  frequently  produce  marked  changes  in  the  char¬ 
acteristics  of  the  finished  product.  These  characteristics  will 
be  taken  up  later. 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS’  HALL,  LONDON 

§  40 


STEEL  AND  OTHER  METALS 


§40 


9 


IRON 


PRODUCTION  OF  IRON 

2.  Ores  of  Iron. — Iron  exists  in  nature  as  an  ore,  which 
is  a  combination  of  iron  and  other  elements  in  the  form  of  rock 
or  earth.  Frequently,  the  iron  is  not  distinguishable  except 
by  chemical  analysis.  The  only  ores  from  which  iron  is 
manufactured  in  large  quantities  are  those  containing  the 
oxides  and  carbonates  of  iron,  the  oxides  being  the  richer  in 
iron.  The  ore  known  as  magnetite ,  Fe304,  contains  about 
72  per  cent,  of  iron;  that  known  as  red  hematite ,  Fe203,  con¬ 
tains  about  70  per  cent,  of  iron;  while  another  ore,  brown 
hematite ,  2Fe203-\-?>H20  contains  about  60  per  cent,  of  iron. 
These  constitute  the  valuable  oxide  ores.  The  carbonate 
ore,  ferrous  carbonate,  FeC03,  contains  about  48  per  cent, 
of  iron. 

Magnetite  is  black  and  brittle  and  often  has  magnetic  proper¬ 
ties,  from  which  characteristic  it  derives  its  name,  Red  hema¬ 
tite  varies  in  color  from  a  deep  red  to  a  steel  gray,  but  all 
varieties  make  a  red  streak  when  drawn  across  unglazed 
porcelain.  On  account  of  its  abundance  and  the  character  of 
the  iron  it  yields,  red  hematite  is  the  most  important  of  the 
ores  of  iron.  Brown  hematite  varies  in  color  from  a  brownish 
black  to  a  yellowish  brown.  The  carbonate  varies  in  color 
from  yellow  to  brown,  but  the  light-colored  ore  rapidly 
becomes  brown  when  exposed  to  the  air.  This  ore  is  reduced 
to  Fe203  by  roasting  and  exposure  to  the  air,  which  drives 
off  the  carbon  dioxide  and  water,  as  well  as  much  of  the 
sulphur  and  arsenic,  when  these  are  present.  The  carbonate 
is  thus  changed  to  an  oxide  having  the  same  composition 
as  red  hematite. 

3.  Separation  of  Iron  From  Its  Ores. — Iron  in  the 
metallic  form  is  extracted  from  the  ores  by  the  action  of 
heat.  The  ores  are  first  heated  at  a  comparatively  low 
temperature,  so  as  to  drive  off  all  moisture  and  volatile 
matter  that  may  be  present.  Then  they  are  heated  to  a 


§40 


STEEL  AND  OTHER  METALS 


3 


comparatively  high  temperature,  in  the  presence  of  either  car¬ 
bon,  C ,  or  carbon  monoxide,  CO.  At  this  higher  temperature, 
the  oxygen  of  the  ore  combines  with  the  carbon  or  carbon 
monoxide  to  form  carbon  dioxide,  C02 ,  thus  leaving  the  iron 
chemically  free.  This  process  is  known  as  the  reduction 
process ,  since  the  ores  are  reduced,  or  deprived  of  their 
oxygen  and  other  non-metallic  substances,  leaving  the  metal 
itself  quite  free. 

The  fuels  used  to  produce  the  high  temperatures  in  the 
reduction  process  are  wood,  soft  coal,  hard  coal,  coke,  and 
gas.  The  heating  is  done  in  a  furnace  lined  with  some 
material,  such  as  firebrick,  which  is  not  easily  affected  by 
great  heat.  The  ores  charged  into  the  furnace  usually 
contain  silica,  alumina,  or  some  other  substance  that  is 
difficult  to  remove,  except  by  chemical  combination  with 
another  substance  put  in  especially  for  that  purpose  and 
known  as  a  flux.  The  flux  unites  with  the  impurities  in  the 
ore  and  becomes  fluid,  when  it  is  known  as  slag.  The  slag 
is  lighter  than  the  molten  iron,  and  consequently  floats 
on  the  surface  of  the  iron,  from  which  it  may  be  removed 
either  by  tapping  off  the  iron  from  below  and  leaving  the 
slag  to  be  drawn  later,  or  by  drawing  off  the  slag  through  a 
tap  hole  at  the  surface  of  the  molten  liquid,  without 
disturbing  the  iron  below. 

4.  Blast  Furnace. — All  iron  used  for  manufacturing 
purposes  is  obtained  by  reducing  the  ores  of  iron  in  a  special 
furnace  called  a  blast  furnace.  The  furnace  consists  of  a 
slightly  tapering  circular  shell,  built  up  of  iron  plates  and 
lined  with  firebrick.  The  lower  end  of  this  shell  is  cone- 
shaped,  with  the  small  end  of  the  cone  pointing  downwards. 
When  the  furnace  is  in  operation,  this  is  the  region  of  highest 
temperatures,  where  most  of  the  melting  takes  place. 

The  ore,  fuel,  and  flux  are  charged  into  the  furnace  at 
the  top,  through  an  opening  that  can  be  closed  by  an  iron 
cone  so  as  to  prevent  the  escape  of  gases.  The  lowest  tem¬ 
peratures  exist  near  the  top  of  the  furnace,  the  mass  growing 
gradually  hotter  as  it  descends.  As  fast  as  the  metal  at 


4 


STEEL  AND  OTHER  METALS 


§40 


the  bottom  melts,  the  charge  above  settles,  being  regularly 
replenished  by  charging  at  the  top.  Thus  there  is  a  con¬ 
tinuous  downward  movement  of  the  charge. 

As  the  charge  in  the  blast  furnace  descends  into  the  zone 
of  greater  temperatures,  the  reduction  process  takes  place, 
and  the  molten  iron  collects  at  the  bottom.  The  slag,  which 
contains  much  of  the  impurities  and  undesirable  substances 
carried  in  the  ore,  collects  just  above  the  mass  of  molten 
iron,  since  it  is  lighter  than  iron.  This  is  especially  advan¬ 
tageous,  since  it  protects  the  iron  from  the  oxidizing  effect 
of  the  hot  blast  entering  the  furnace.  The  slag  is  usually 
drawn  off  at  intervals  through  openings  near  the  surface  of 
the  molten  iron. 

The  air  blast,  by  means  of  which  the  combustion  is  hastened 
and  the  higher  temperatures  obtained,  is  furnished  by  blowing 
engines.  It  enters  near  the  base  of  the  furnace,  through 
nozzles  or  so-called  tuyeres ,  at  a  pressure  of  from  5  to  15  pounds 
per  square  inch.  As  the  blast  passes  up  through  the  charge, 
the  oxygen  of  the  heated  air  combines  with  the  carbon  of 
the  fuel,  forming  carbon  monoxide,  CO,  since  the  amount 
of  oxygen  present  is  insufficient  to  form  carbon  dioxide,  C02. 
As  carbon  monoxide  is  quite  combustible,  it  is  conveyed  by 
a  pipe  from  the  top  of  the  furnace  to  one  of  the  reheating 
stoves  instead  of  being  allowed  to  escape  at  once  into  the 
atmosphere. 

The  stoves  are  iron  shells  lined  with  firebrick,  each  one 
containing  two  vertical  chambers,  the  combustion  chamber 
and  the  checkerwork ,  the  latter  consisting  of  numerous 
columns  of  firebrick  intended  to  provide  a  large  contact 
area  for  the  passing  gases.  The  carbon  monoxide  from  the 
blast  furnace  is  periodically  led  into  one  or  the  other  of  the 
stoves,  where,  during  its  combustion,  it  will  heat  the  checker- 
work.  The  gas  is  then  turned  oft  and  air  is  sent  through, 
thus  heating  it  before  it  enters  the  furnace. 

5.  Pig  Iron. — After  the  blast  furnace  has  been  started, 
it  is  continuous  in  its  operation,  the  molten  iron  being  drawn 
oft  at  regular  intervals  through  a  tap  hole  in  the  bottom  of 


§40 


STEEL  AND  OTHER  METALS 


5 


the  furnace.  In  the  sand  floor  that  surrounds  the  base  of  the 
furnace  and  sloping  away  from  it,  a  long  trench  is  dug, 
leading  away  from  the  tap  hole  from  which  the  molten  iron 
is  drawn.  From  this  trench,  branch  trenches  are  dug  at 
intervals,  and  these  branches  lead  to  numerous  smaller 
trenches,  or  molds,  about  3  feet  long  and  from  3  to  4  inches 
wide  and  deep.  When  sufficient  molten  iron  has  collected  in 
the  bottom  of  the  furnace,  the  blast  is  shut  off  and  the  tap  hole 
opened,  thus  permitting  the  iron  to  run  out  and  fill  the 
trenches  and  molds.  The  tap  hole  is  then  plugged,  and  the 
blast  again  turned  on.  The  molten  iron,  on  cooling,  is  known 
as  pig  iron. 

Pig  iron  contains  from  3  to  10  per  cent,  of  impurities,  of 
which  the  larger  part  is  carbon,  although  silicon,  sulphur, 
manganese,  phosphorus,  and  other  elements  may  be  present. 
Pig  iron  is  usually  classified  according  to  its  condition,  the 
impurities  it  contains,  and  the  purposes  for  which  it  is  to  be 
used.  It  is  especially  valuable  because  it  melts  and  becomes 
quite  fluid  at  a  temperature  of  about  2,200°  F.,  which  is 
readily  attainable  in  a  foundry  cupola.  This  property  of 
pig  iron,  combined  with  its  relative  cheapness  and  its  exten¬ 
sive  use  in  the  manufacture  of  wrought  iron  and  steel,  makes 
it  the  most  useful  form  of  iron. 


CAST  IRON 

•  \ 

6.  Foundry  Cupola. — In  making  iron  castings,  pig  iron 
is  melted  in  a  special  form  of  melting  furnace  called  a  cupola, 
and  is  then  poured  into  molds  of  sand.  After  it  has  solidi¬ 
fied,  it  is  known  as  cast  iron.  The  pig  iron  that  is  melted 
in  the  cupola  and  used  in  foundry  work  is  known  as  foundry  pig. 

The  cupola  has  an  outer  shell  of  iron  plates  firmly  riveted 
together.  The  tall  cylinder  thus  formed  is  lined  with  fire¬ 
brick.  Near  the  bottom,  the  cupola  is  surrounded  by  a 
ring-shaped  metal  box,  which  through  various  orifices  supplies 
the  necessary  amount  of  air  under  pressure.  The  cupola 
is  charged  with  alternate  layers  of  coke  and  pig  iron,  and  as 


0 


STEEL  AND  OTHER  METALS 


§40 


the  iron  in  the  lower  end  melts,  it  is  drawn  oft  through  a 
tap  hole  into  ladles  and  carried  to  the  molds. 

7.  Characteristics  of  Cast  Iron. — Cast  iron  is  a  metal 
of  crystalline  formation,  very  strong  in  compression  and 
comparatively  weak  in  tension.  There  are  several  grades 
of  cast  iron  that  differ  chiefly  in  the  amount  of  carbon  con¬ 
tained,  although  distinctive  properties  are  given  to  the  iron 
by  other  elements,  such  as  silicon,  sulphur,  phosphorus,  and 
manganese. 

8.  Carbon  in  Cast  Iron. — Cast  iron  usually  contains 
from  2  to  4^  per  cent,  of  carbon,  but  when  there  is  a  large 
percentage  of  manganese  present  there  may  be  6  per  cent, 
or  more  of  carbon.  The  quality  of  cast  iron  depends  largely 
on  the  condition  of  the  carbon  present  in  the  iron.  Carbon 
exists  in  cast  iron  in  two  forms,  namely,  combined  carbon  and 
graphitic  carbon.  In  iron  containing  combined  carbon,  the 
appearance  of  the  fracture,  when  a  piece  is  broken,  is  silvery 
white;  while,  if  an  iron  containing  graphitic  carbon  is  broken, 
it  shows  a  dark-gray  fracture. 

The  melting  point  of  gray  iron  is  about  2,200°  F.,  and  that 
of  white  iron,  about  2,000°  F.  The  average  value  of  the  tensile 
strength  of  cast  iron  is  about  15,000  pounds  per  square  inch, 
and  that  of  the  compressive  strength  about  80,000  pounds  per 
square  inch.  The  gray  iron,  which  contains  graphitic  car¬ 
bon,  is  weaker  in  both  tension  and  compression  than  the 
white  iron,  which  contains  combined  carbon.  But  since  the 
white  iron  is  very  hard  and  brittle,  it  is  difficult  to  work, 
and  consequently  the  softer  gray  iron  is  most  generally  used. 
A  cubic  foot  of  dark-gray  iron  weighs  about  425  pounds,  and 
a  cubic  foot  of  white  iron  about  475  pounds.  The  appear¬ 
ance  of  the  fracture  of  the  different  grades  of  cast  iron 
varies  from  a  coarse  semicrystalline  gray  to  a  fine  close- 
grained  white. 

9.  Silicon,  Sulphur,  Phosphorus,  and  Manganese 
in  Cast  Iron. — Silicon  in  small  proportions  tends  to  increase 
the  strength  and  hardness  of  cast  iron,  and  aids  in  prevent- 


§40 


vSTEEL  AND  OTHER  METALS 


7 


in g  the  formation  of  blowholes  in  castings.  Sulphur  tends 
to  make  the  iron  hard  and  brittle.  On  the  other  hand, 
this  element  makes  the  iron  more  fusible.  Phosphorus  also 
makes  the  iron  more  fusible,  tends  to  prevent  blowholes,  and 
is  supposed  to  prevent  shrinkage  in  cooling,  so  that  the  iron 
fills  the  mold  more  perfectly.  On  the  other  hand,  phos¬ 
phorus  makes  the  iron  brittle  and  liable  to  break  under 
suddenly  applied  loads.  Manganese  has  the  property  of 
increasing  the  amount  of  combined  carbon  in  cast  iron,  and 
thus  gives  a  harder  iron,  rendering  it  less  plastic  and  more 
brittle.  It  also  increases  the  shrinkage.  However,  manga¬ 
nese  unites  readily  with  sulphur,  and  thus  tends  to  remove 
the  latter  from  iron. 


WROUGHT  IRON  * 

10.  Purity  of  Wrought  Irou. — Of  all  the  forms  of 
iron  obtained  from  the  ores  by  processes  of  manufacture, 
wrought  iron  is  the  purest.  It  not  only  contains  very  little 
or  no  carbon,  but  the  best  grades  are  also  free  from  the  other 
impurities  so  common  to  cast  iron  and  steel.  Wrought  iron 
can  be  produced  either  from  the  ore  directly  or  by  the  con¬ 
version  of  pig  iron  in  a  reverberatory  furnace.  In  the  latter 
process,  called  the  puddling  process ,  white  pig  iron  is  melted 
and  subjected  to  an  oxidizing  flame  until  the  carbon  is  burned 
out  or  becomes  less  than  1  per  cent. 

11.  Puddling  Furnace. — The  most  common  type  of 
reverberatory,  or  puddling,  furnace  consists  of  an 
arched  chamber  of  firebrick  containing  a  shallow  receptacle, 
the  hearth,  which  may  hold  from  1,000  to  1,500  pounds  of 
molten  metal,  and  a  grate.  The  gases  produced  by  the  fuel 
burning  on  this  grate  pass  over  the  hearth  into  a  flue.  The 
heat  is  reflected  downwards  by  the  arched  top  of  the  furnace, 
making  the  material  on  the  hearth  extremely  hot,  the  iron 
being  worked  at  temperatures  ranging  from  2,500°  F.  to 
3,000°  F.  Pig  iron  is  generally  used  for  the  charge;  it  con¬ 
tains  from  3  to  10  per  cent,  of  impurities,  while  the  wrought 
iron  produced  contains  less  than  1  per  cent.  The  loss  of  iron 

211—33 


8 


STEEL  AND  OTHER  METALS 


§40 


in  the  process  is  comparatively  small.  Scrap  iron,  machine- 
shop  borings  and  turnings,  etc.  are  used  as  a  charge  when  the)" 
are  available;  and,  as  they  are  in  a  finely  divided  state,  a 
heat  may  be  finished  in  20  minutes,  while  with  a  charge  of 
pig  iron  it  requires  from  1^  to  2  hours. 

12.  Puddling  and  Rolling. — The  iron  is  heated  in  the 
furnace  until  it  melts  into  a  thick,  fluid  mass.  While  in  this 
condition,  it  is  thoroughly  stirred  and  worked  by  means  of 
a  long  iron  bar,  to  insure  all  parts  of  the  iron  being  treated. 
This  working  is  called  rabbling.  The  puddling  process,  which 
is  carried  on  at  a  high  temperature  with  the  iron  in  a  fluid 
state,  causes  most  of  the  impurities  to  be  burned  out,  or  else 
separated  as  slag.  When  the  process  is  nearly  completed, 
the  iron  becomes  thicker  and  is  known  as  a  mat.  The  work¬ 
man  divides  this  mat  into  masses  of  about  160  pounds  each, 
and  then  with  a  bar  rolls  them  into  balls  on  the  hearth  of  the 
furnace.  A  small  amount  of  slag  will  adhere  to  the  balls  and 
be  rolled  up  in  them.  Consequently,  as  fast  as  they  are 
formed,  these  balls  are  removed  from  the  furnace  and  passed 
through  a  squeezer ,  which  is  a  form  of  press.  This  operation 
forces  out  most  of  the  slag  remaining  in  the  ball,  and  welds 
the  iron  into  a  solid  mass,  after  which  it  is  passed  through 
rolls.  The  rolling  process  works  out  more  slag  and  reduces 
the  iron  to  the  form  of  bars.  These  bars  are  then  reheated 
and  rerolled  to  improve  their  quality. 

13.  Properties  of  Wrought  Iron. — At  a  temperature 
of  1,500°  F.  or  1,600°  F.,  wrought  iron  softens;  and  if  the  • 
surfaces  of  two  pieces  thus  heated  are  brought  together,  with 
a  flux  to  remove  the  oxide  formed  on  the  surfaces,  the  separate 
pieces  can  be  welded  or  made  to  unite  into  one  piece  by 
hammering  or  pressing. 

Good  wrought  iron  can  easily  be  forged  and  welded,  but 
only  with  great  difficulty  can  it  be  melted  and  poured  into 
molds,  like  cast  iron  and  steel,  since  its  melting  point  is 
about  3,000°  F.  When  broken  by  a  tensile  force,  its  fibrous 
structure  is  plainly  apparent.  When  subjected  to  repeated 
shocks  or  loads  that  exceed  the  elastic  limit,  the  structure 


§40 


STEEL  AND  OTHER  METALS 


9 


changes  and  becomes  more  crystalline.  Wrought  iron  has 
a  greater  tensile  strength  than  cast  iron,  and  can  withstand 
shocks  much  better.  The  tensile  strength  of  good  wrought 
iron  is  about  50,000  pounds  per  square  inch.  When  cold- 
rolled  under  great  pressure,  the  strength  of  the  material  is 
greatly  increased. 

14.  Wrought  iron  may  contain  as  much  carbon  as  mild 
steel,  but  it  is  far  more  fibrous  and  less  crystalline  than  steel. 
This  is  due  to  the  manner  in  which  it  is  made,  the  successive 
squeezing  and  rolling  having  a  tendency  to  cause  the  fibers 
of  the  iron  to  lie  parallel  to  the  direction  in  which  the  bar 
is  rolled.  A  small  amount  of  slag  remains  in  the  finished 
product,  rolled  out  into  fibers  that  lie  between  the  fibers  of 
the  iron. 

The  different  grades  of  wrought  iron  are  termed  common 
bar  iron,  best  iron,  double  best ,  and  triple  best,  according  to  the 
amount  of  working  each  receives.  The  quality  of  the  pig 
iron  and  the  methods  of  manufacture  also  influence  the  quality 
of  the  wrought  iron.  Thus,  Swedish  iron  is  generally  con¬ 
sidered  to  be  the  best  wrought  iron,  because  high-grade  stock 
is  used  and  great  care  is  exercised  in  its  manufacture.  This 
grade,  however,  is  too  expensive  for  most  classes  of  work. 

15.  Defects  in  Wrought  Iron. — Wrought  iron  pro¬ 
duced  from  poor  ore  and  having  an  excess  of  phosphorus  is 
said  to  be  cold  short;  that  is,  it  is  very  brittle  when  cold,  and 
is  liable  to  crack  when  bent.  It  can,  however,  be  worked 
very  well  at  high  temperatures.  If  the  iron  contains  sulphur, 
it  is  said  to  be  hot  short,  or  brittle  and  liable  to  drack  when 
hot,  although  fairly  good  when  cold.  Hot-short  iron,  some¬ 
times  called  red  short,  is  useless  for  welding,  but  it  is  tough 
when  cold  and  is  used  extensively  in  making  tin  plate.  In 
order  to  test  wrought  iron  for  hot-shortness,  a  sample  may 
be  raised  to  a  white  heat  and  an  attempt  made  to  forge  and 
weld  it. 


10 


STEEL  AND  OTHER  METALS 


§40 


STEEL 

16.  Definition  of  Steel.' — It  is  a  difficult  matter  to  give 
a  concise  definition  of  steel  that  will  include  all  the  grades 
produced,  and  will  at  the  same  time  exclude  cast  iron  and 
wrought  iron.  However,  steel  is  essentially  an  alloy  of  iron 
and  small  percentages  of  carbon,  the  latter  being  present  in 
greater  quantities  than  in  wrought  iron  and  in  smaller  quanti¬ 
ties  than  in  cast  iron.  Small  percentages  of  other  elements 
are  often  added  in  order  to  give  special  properties  to  the 
product.  The  question  of  the  proper  classification  of  steels 
has  been  given  much  attention,  but  thus  far  no  classification 
proposed  has  been  generally  adopted. 

There  are  several  substances,  such  as  nickel,  tungsten, 
chromium,  manganese,  molybdenum,  aluminum,  etc.,  that 
have  great  influence  on  the  quality  of  the  steel  containing 
them.  Some  of  these  are  added  to  the  molten  metal  during 
the  process  of  manufacture,  for  the  purpose  of  modifying  its 
quality  to  meet  certain  requirements.  Others  of  these  sub¬ 
stances  may  exist  in  the  steel  as  objectionable  impurities, 
which  are  derived  either  from  the  ore  or  the  fuel,  or  from  both. 


MANUFACTURE  OF  STEEL 

17.  Steel  used  for  manufacturing  purposes  may  be  made 
by  any  one  of  three  processes,  known  as  the  open-hearth 
process ,  the  Bessemer  process ,  and  the  crucible  process. 

18.  Open-Heartli  Process. — In  the  open-hearth 

process,  steel  is  made  by  melting  a  charge  of  pig  iron  with 
wrought  iron  or  steel  scrap,  or  by  melting  pig  iron  and  iron 
ore  in  an  oxidizing  flame  to  remove  the  excess  of  carbon. 
The  furnace  is  termed  open-hearth  because  it  is  open  at  both 
ends.  It  consists  of  a  rectangular  hearth,  about  twice  as  long 
as  wide,  made  of  firebrick,  silica  brick,  and  other  refractory 
material.  The  roof  is  arched,  so  as  to  deflect  the  flame  on 
to  the  charge.  In  the  open-hearth  process,  the  excess  carbon 
in  the  charge  is  burned  out  until  only  the  desired  percentage 


§40 


STEEL  AND  OTHER  METALS 


11 


remains,  at  which  point  the  process  is  stopped.  Gaseous 
fuel  is  used,  and  (except  in  the  case  of  natural  gas)  both  the 
gas  and  the  air  before  igniting  are  highly  heated  by  the 
waste  gases  in  regenerative  furnaces. 

Open-hearth  steel  is  used  for  the  better  grades  of  steel 
plate,  forgings,  machine  shafts,  car  axles,  structural  steel, 
etc.  In  fact,  the  steel  made  by  this  process  is  superior  for 
all  work  to  that  made  by  the  Bessemer  process. 

19.  The  open-hearth  process  divides  itself  into  the  acid 
and  the  basic  systems.  In  the  former,  the  hearth  is  made  of 
acid  material — silica  in  the  form  of  silica  sand  or  silica  brick. 
In  the  latter,  the  hearth  and  such  portions  of  the  side  walls 
as  the  slag  is  likely  to  come  in  contact  with  are  made  of  basic 
material,  such  as  magnesite  or  dolomite.  The  hearth  is  inert, 
taking  no  part  in  the  reactions  of  the  process,  and  must 
therefore  be  made  of  a  material  to  correspond  with  the 
character  of  the  slag  produced. 

In  the  acid  process,  only  stock  containing  relatively 
small  amounts  of  phosphorus  and  sulphur  can  be  used,  as 
with  an  acid  slag  these  impurities  are  not  eliminated,  or  only 
to  a  small  extent.  For  this  reason,  the  field  of  the  acid 
process  is  limited. 

The  basic  process  differs  from  the  acid  one  in  that  stock 
higher  in  phosphorus  and  sulphur  is  treated,  and  basic  mate¬ 
rials,  usually  lime,  are  added,  so  as  to  give  a  slag  that  will 
effect  purification.  The  only  difference  in  the  apparatus  used 
is  that  the  hearth  is  made  of  basic  instead  of  a  silicious  material. 
The  function  of  the  slag  is  to  form  a  blanket,  or  covering,  for 
the  molten  metal,  protecting  it  from  oxidation  and  loss  of 
heat  and  oxygen,  for  the  removal  of  silicon,  manganese, 
carbon,  etc. 

20.  Bessemer  Process. — The  Bessemer  process 
consists  in  decarburizing,  or  taking  out  the  carbon  from,  a 
charge  of  pig  iron  by  forcing  a  blast  of  air  through  it  while  in 
a  molten  condition.  The  oxygen  of  the  air  unites  with  the 
carbon,  carrying  off  the  latter  as  C02.  A  quantity  of  pig  iron 
rich  in  carbon  and  free  from  objectionable  impurities  is  then 


12 


STEEL  AND  OTHER  METALS 


§40 


added,  so  as  to  give  just  the  required  percentage  of  carbon 
to  the  steel,  this  operation  being  known  as  recarburizing. 
The  molten  metal  is  then  poured  into  ingot  molds,  and  the 
cold  blocks  of  metal,  when  taken  from  the  molds,  are  known 
as  ingots.  These  are  afterwards  heated  and  rolled  into  com¬ 
mercial  shapes. 

Bessemer  steel  is  used  for  rails,  nails,  structural  shapes, 
etc.,  wherever  its  cheapness  makes  it  desirable  and  wherever 
it  will  be  just  as  satisfactory  as  the  higher  grade  and  more 
expensive  open-hearth  steel. 

2 1 .  The  decarburizing  and  recarburizing  processes  used  in 
making  Bessemer  steel  are  carried  on  in  a  vessel  known  as  a 
Bessemer  converter.  The  converter  consists  of  a  shell  of  heavy 
steel  plate  riveted  together  and  lined  with  refractory  material. 
It  is  hung  on  hollow  trunnions,  through  which  the  air  blast 
may  be  conveyed  to  a  receptacle  at  the  bottom  of  the  vessel. 
From  here,  suitable  pipes,  called  tuyeres,  lead  the  air  to  the 
metal.  The  vessel  is  rotated  by  hydraulic  power  applied 
through  a  rack  and  pinion.  The  construction  is  such  that  it 
can  be  made  to  revolve  completely  and  empty  out  any  slag 
after  pouring  the  steel.  Converters  are  made  in  various 
sizes,  having  capacities  of  from  1  to  20  tons.  The  metal  fills 
only  a  small  part  of  the  space,  as  the  reaction  is  so  violent 
that  considerable  room  must  be  allowed  for  it. 

22.  Crucible  Process. — The  oldest  and  simplest  proc¬ 
ess  of  steel  manufacture  is  the  crucible  process.  In 
this  process,  the  stock  is  melted  in  a  crucible,  which  is  heated 
by  a  fire  of  coke,  hard  coal,  or  gas.  The  air  supply  is  heated 
in  regenerative  chambers.  The  iron  that  is  melted  to  form 
the  steel  may  be  either  high  in  carbon,  requiring  no  addition 
of  carbon,  or  low  in  carbon,  requiring  recarburizing.  The 
stock  used  is  chiefly  wrought  iron  and  steel  scrap,  with  suffi¬ 
cient  charcoal  to  give  the  required  percentage  of  carbon. 

It  is  maintained  that  the  highest  grade  of  crucible  steel 
can  be  manufactured  only  from  blister  steel  made  from  the 
purest  Swedish  iron.  As  no  sulphur  nor  phosphorus  is 


STEEL  AND  OTHER  METALS 


13 


§40 

removed  from  the  charge  during  the  melting  process,  the 
stock  must  be  free  from  these  impurities. 

In  American  practice,  the  crucible  is  filled  with  the  stock 
while  cold  and  before  inserting  it  in  the  heating  furnace. 
The  time  required  for  melting  varies  from  2\  to  3  hours. 
Soft  steel,  or  steel  low  in  carbon,  requires  a  longer  time  to 
melt  than  high-carbon  steel.  The  presence  of  manganese, 
however,  shortens  the  period  of  melting.  For  making  tool 
steel,  the  molten  contents  of  the  crucibles  are  poured  into 
ingot  molds,  that  are  about  3  or  4^  inches  square  and  deep 
enough  to  hold  the  steel  from  one  or  more  crucibles.  These 
molds  open  lengthwise,  so  that  the  ingot  may  be  easily 
removed.  The  cost  of  making  steel  by  the  crucible  process  is 
higher  than  by  either  the  open-hearth  or  the  Bessemer  proc¬ 
ess,  for  which  reason  crucible  steel  is  used  only  in  the  manu¬ 
facture  of  tools  and  in  other  cases  where  its  high  cost  is 
compensated  by  the  better  quality  of  the  product. 

23.  Comparative  Value  of  tlie  Several  Classes  of 
Steel. — The  Bessemer  process  was  the  first  to  be  perfected,  and 
for  35  years,  or  up  to  about  1890,  it  led  the  open-hearth, 
both  as  to  tonnage  produced  and  in  the  perfection  of  methods 
and  appliances — both  metallurgical  and  mechanical.  While 
the  Bessemer  process  is  the  older,  this  is  the  only  direction 
in  which  it  can  claim  superiority  over  the  open-hearth.  In 
the  order  of  their  metallurgical  and  commercial  importance 
today,  the  processes  rank:  first,  the  open-hearth;  second,  the 
Bessemer;  and  third,  the  crucible. 

The  open-hearth  process  can  claim  as  its  own  a  larger 
field  than  the  Bessemer.  Open-hearth  steel  is  now  used  for 
the  better  grades  of  plate  steel,  forgings,  car  axles,  and 
structural  steel.  The  basic  open-hearth  process  is  used 
where  an  extra-soft,  pure  steel  is  required,  as  in  plates, 
sheets,  rods,  wires,  etc. 

Bessemer  steel  is  used  for  rails,  nails,  tin  plate,  light  axles, 
and,  in  fact,  for  all  articles  where  cheapness  is  desired.  This 
grade  of  steel,  however,  is  being  rapidly  replaced  by  steel 
produced  by  the  basic  open-hearth  process.  The  basic 


14 


STEEL  AND  OTHER  METALS 


§40 


process,  by  cheaper  production  than  was  possible  in  the 
acid  open-hearth,  is  a  formidable  rival  of  the  Bessemer,  and 
seems  practically  sure  to  supplant  it  largely  in  the  next 
few  years.  Owing  to  lower  cost  of  production,  the  Bessemer 
process  held  undisputed  sway  for  years  in  all  lines  using  a 
large  tonnage  of  steel.  The  open-hearth  gradually  demon¬ 
strated  its  superior  fitness  for  special  lines.  While  both  the 
crucible  and  the  open-hearth  process  have  distinctive  fields, 
the  Bessemer  has  no  field  the  open-hearth  cannot  fill,  and 
only  by  lower  cost  does  it  still  produce  the  greater  tonnage. 
A  large  proportion  of  rails  are  still  made  of  Bessemer  metal. 

While  the  crucible  process  is  of  the  least  consequence, 
it  holds  the  most  distinctive  field  metallurgically,  and  one 
from  which  the  others  seem  unlikely  to  crowd  it  out.  Given 
the  same  composition,  it  is  well  established  that  crucible 
steel  is  superior  to  either  of  the  others,  but  owing  to  the 
much  higher  cost  of  production,  its  use  is  now  restricted 
mainly  to  the  making  of  high-grade  tools,  certain  mining 
drills,  parts  of  intricate  machines,  and,  in  general,  where  the 
first  cost  of  the  steel  can  be  ignored. 


BLISTER  STEEL  AND  SHEAR  STEEL 

24.  Blister  Steel. — Wrought-iron  bars  that  have  been 
treated  by  a  cementation  process  are  known  as  blister  steel. 
This  treatment  consists  in  heating  the  bars  to  a  high  temper¬ 
ature  for  several  hours  in  an  air-tight  compartment  of  a 
furnace  and  in  contact  with  carbon.  The  carbon  enters  the 
iron,  converting  it  into  steel  to  a  greater  or  less  depth,  depend¬ 
ing  on  the  length  of  time  the  process  is  continued.  The 
surfaces  of  the  bars  become  rough  and  spotted  with  blisters, 
and  the  product  thus  becomes  known  as  blister  steel.  It  i's 
made  in  several  grades,  depending  on  the  percentage  of 
carbon  absorbed,  which  usually  varies  from  .5  to  1.5  per  cent. 

25.  Shear  Steel. — Blister  steel  is  used  in  making 
shear  steel.  A  number  of  bars  of  blister  steel  are  welded 
together  so  as  to  form  a  single  large  bar,  which  is  then  ham- 


§40 


STEEL  AND  OTHER  METALS 


15 


mered  or  rolled  down  to  the  desired  dimensions.  Shear  steel 
is  made  in  different  grades,  as  single  shear ,  double  shear ,  etc., 
each  successive  and  higher  grade  being  produced  by  cutting 
the  bars  of  the  next  lower  grade,  welding  them  together, 
and  working  to  size.  Both  blister  steel  and  shear  steel  are 
frequently  used  in  making  crucible  steel. 


ALLOT  STEELS 

26.  Tungsten  Steel. — When  elements  other  than  carbon 
are  added  to  steel  to  give  it  special  properties,  the  product 
is  called  an  alloy  steel. 

One  of  the  most  important  of  these  elements  is  tungsten, 
and  a  steel  in  which  the  principal  properties  are  due  to 
this  element  is  known  as  tungsten  steel.  The  amount 
of  tungsten  may  vary  from  .1  to  10  per  cent.,  the  usual  amount 
being  from  3  to  5  per  cent.  The  tungsten  is  introduced  into 
the  crucible  in  the  form  of  ferro tungsten,  which  is  simply  an 
alloy  of  iron  and  tungsten.  The  amount  of  manganese  usually 
runs  from  1.5  to  2.5  or  3  per  cent.,  and  the  percentages  of  sili¬ 
con,  sulphur,  and  phosphorus  are  the  same  as  in  carbon  steel. 

27.  Manganese  Steel. — Among  all  the  varieties  of  steel, 
the  hardest  and  toughest  is  manganese  steel.  The  best 
results  are  obtained  with  from  7  to  14  per  cent,  of  manganese. 
The  maximum  strength  is  obtained  with  about  13  or  14  per 
cent,  of  manganese,  and  the  greater  amount  manufactured 
contains  from  12  to  14  per  cent.  This  steel  is  high  in  carbon, 
because  the  ferromanganese  used  in  its  manufacture  is  high 
in  carbon.  The  extreme  hardness  and  toughness  of  man¬ 
ganese  steel  are  secured  by  quenching  it  in  water.  This  is 
one  of  the  most  noticeable  peculiarities  of  this  steel,  since 
the  other  alloy  steels  increase  in  hardness,  but  decrease  in 
toughness,  by  quenching. 

Manganese  steel  is  practically  non-magnetic.  Its  uses  are 
restricted  to  work  that  does  not  require  machining,  such  as 
castings  and  forgings  for  various  purposes.  It  works  readily 
at  a  red  heat,  and  is  used  principally  for  the  jaws  and  plates 


16 


STEEL  AND  OTHER  METALS 


§40 


of  rock  crushers  and  grinding  machinery,  car  wheels,  T  rails, 
safes  and  vaults,  etc.  This  kind  of  steel  may  be  made  in 
crucibles,  but  the  open-hearth  process  is  more  suitable  for 
large  quantities.  Owing  to  the  large  amount  of  manganese 
that  it  contains,  the  metal  is  extremely  fluid,  and  solid 
castings,  both  large  and  small,  are  readily  made.  The  shrink¬ 
age  is  excessive,  being  about  f  inch  to  the  foot,  which 
increases  the  difficulties  of  casting. 

28.  Nickel  Steel. — The  addition  of  nickel  to  steel  will 
greatly  increase  its  strength,  ductility,  and  elasticity.  The 
amount  of  nickel  added  usually  varies  from  3  to  5  per  cent., 
although  alloys  containing  as  high  as  30  per  cent,  are  made. 
The  nickel  is  added  to  the  steel  either  as  metallic  nickel  or 
as  ferronickel,  which  is  charged  with  the  rest  of  the  stock 
into  the  furnace.  Nickel  steel  is  made  almost  entirely  by  the 
open-hearth  process,  though  it  can  be  made  by  either  the 
Bessemer  or  the  crucible  process.  It  is  readily  worked 
either  hot  or  cold  and  is  easily  forged,  but  it  is  harder  to 
machine  than  ordinary  carbon  steel.  It  is  used  extensively 
for  armor  plate,  gun  barrels,  engine  and  propeller  shafts, 
automobile  frames,  and  a  great  variety  of  purposes  in  which 
great  strength  and  lightness  are  required,  and  in  which  high 
cost  is  not  prohibitive.  Nickel  steel  is  also  especially  valuable 
because  it  offers  a  much  greater  resistance  to  corrosive 
influences  than  does  carbon  steel. 


§40 


STEEL  AND  OTHER  METALS 


17 


COPPER,  ZINC,  AND  ALLOYS 

29.  Copper. — The  metal  known  as  copper  is  found 
abundantly  in  nature,  both  free  and  in  chemical  combination, 
in  such  forms  as  cuprous  oxide,  Cu20\  cuprous  sulphide,  Cu2S ; 
and  as  basic  carbonate,  Cu2(0H)2C03.  The  methods  applied 
for  the  extraction  of  copper  vary  with  the  ore  under  treatment. 

Copper  may  be  drawn  into  fine  wire  or  rolled  into  thin 
sheets.  Its  tenacity  is  considerable,  being  next  to  wrought 
iron.  It  is  unaltered  in  dry  air  at  ordinary  temperatures, 
but  it  absorbs  oxygen  in  the  presence  of  moisture  and  carbon 
dioxide.  Green  spots  then  appear  on  the  surface,  constituting 
a  basic  carbonate  of  copper,  which  is  the  compound  commonly 
known  as  verdigris.  At  a  high  temperature,  copper  absorbs 
oxygen  very  eagerly,  being  converted  into  cupric  oxide. 
Weak  acids,  alkalies,  and  saline  solutions  act  on  it  slowly 
in  the  presence  of  air. 

When  hammered  or  rolled,  copper  becomes  stronger, 
but  also  harder  and  more  brittle.  This  brittleness  may  be 
removed  by  reheating  and  cooling  in  water. 

30.  Zinc. — As  a  rule,  metallic  zinc  does  not  occur 
free  in  nature.  The  chief  ores  are  zinc  carbonate,  ZnC03l 
and  zinc  sulphide,  ZnS.  Zinc  is  hard  and  brittle  at  ordinary 
temperatures  and  of  great  durability. 

The  strength  of  iron  has  been  combined  with  the  durability 
of  zinc  in  the  so-called  galvanized  iron.  This  material  is 
manufactured  by  coating  clean  iron  sheets  with  melted 
zinc,  thus  affording  a  protection  much  needed  in  large  towns, 
where  the  oxides  of  sulphur  and  the  acid  emanations  from 
various  factories  greatly  accelerate  the  corrosion  of  unpro¬ 
tected  iron. 

31.  Brass. — An  alloy  of  copper  and  zinc  is  called  brass. 
The  zinc  promotes  solidity,  and  makes  the  alloy  cast  better 


AVERAGE  ULTIMATE  STRENGTHS  OF  MATERIALS,  IN  POUNDS  PER  SQUARE  INCH 


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20  STEEL  AND  OTHER  METALS  §  40 

than  would  copper  alone.  The  alloy  commonly  used  for 
brass  castings  is  composed  of  66  parts,  by  weight,  of  copper 
and  34  parts  of  zinc,  although  from  2  to  4  per  cent,  of  tin  is 
often  added  to  give  strength  to  the  casting.  The  maximum 
ductility  is  secured  with  about  25  per  cent,  of  zinc.  The 
color  of  brass  varies  from  a  copper  red  to  a  gray,  according 
to  the  amount  of  zinc  used.  Ordinary  yellow  brass  contains 
about  30  per  cent,  of  zinc. 

32.  Bronze. — An  alloy  of  copper  and  tin  is  called  bronze. 
Tin  increases  the  fluidity  of  molten  copper  and  the  tensile 
strength  of  the  casting,  but  decreases  its  ductility.  The 
quality  of  bronze  depends  on  its  composition,  the  purity  of 
the  materials  used,  and  the  care  exercised  in  melting  and 
pouring.  The  maximum  tensile  strength  is  attained  when 
the  alloy  contains  about  18  per  cent,  of  tin,  and  the  maximum 
ductility  when  it  contains  about  4  per  cent,  of  tin.  Bronze 
is  harder,  denser,  and  stronger  than  copper  and  does  not 
oxidize  so  easily. 

33.  Phosphor-Bronze. — Another  alloy  of  copper  and 
tin  containing  a  very  small  percentage  of  phosphorus  is  known 
as  phosphor-bronze.  The  phosphorus  increases  the  strength, 
ductility,  and  solidity  of  castings.  Copper  oxide  forms  in 
nearly  all  alloys  containing  much  copper  when  they  are  being 
melted,  and  thus  reduces  the  strength  and  ductility  of  the 
alloy.  The  addition  of  phosphorus  just  before  pouring  the 
metal  reduces  the  copper  oxide  and  makes  the  casting  more 
ductile. 

34.  Manganese  Bronze. — An  alloy  of  copper  and  man¬ 
ganese  is  called  manganese  bronze.  This  alloy  often  contains 
some  iron  and  may  also  contain  tin.  As  manganese  has  a 
great  affinity  for  oxygen,  it  tends  to  make  a  clear  alloy, 
free  from  copper  oxide.  Manganese  bronze  has  great  strength 
and  will  not  corrode  easily.  Some  so-called  -manganese 
bronzes  contain  no  manganese,  but  are  alloys  of  copper  and 
tin  with  traces  of  other  metals. 


§40 


STEEL  AND  OTHER  METALS 


21 


35.  Application  of  Table  I. — Table  I  gives  the  average 
ultimate  strengths  of  the  various  metals  employed  in  building 
construction.  Its  application  is  shown  by  means  of  the 
following  examples: 

Example  1. — What  pull  will  be  required  to  break  a  wrought-iron 
rod  2  inches  in  diameter? 


Solution. — The  area  of  the  rod  is  .7854X22  =3.14  sq.  in.;  the 
ultimate  tensile  strength  of  wrought  iron,  according  to  Table  I,  is 
48,000  lb.  per  sq.  in.  Therefore,  the  rod  will  break  at  a  stress  of 
3.14X48,000=150,720  lb.  Ans. 

Example  2. — What  length  of  wrought-iron  bar,  if  hung  by  one  end, 
will  break  of  its  own  weight,  assuming  the  weight  of  1  cubic  inch  of 
wrought  iron  to  be  .227  pound? 


Solution. — Assume  any  size  of  bar;  say,  lg  in.  in  diameter.  The 
area  of  this  bar  is  .99  sq.  in.,  which  may,  for  convenience,  be  called 
1  sq.  in.  Now,  as  there  is  just  1  cu.  in.  in  each  linear  inch  in  the  rod, 
a  length  of  1  ft.  will  weigh  .277  X  12  =  3.324  lb.  The  tensile  strength 
of  wrought  iron  being  48,000  lb.  per  sq.  in. ,  and  1  ft.  of  its  length  weigh¬ 


ing  3.324  lb.,  the  length  of  rod  required  is 


48,000 

3.324 


=  14,440.4  ft. 


Ans. 


LOADS  IN  STRUCTURES 


FLOOR,  ROOF,  AND  WIND  LOADS 


DEAD  LOAD 

1.  The  weight  of  the  material  used  in  the  permanent 
structure  of  a  building  produces  loads  on  the  floor  systems, 
the  columns,  and  the  foundations.  These  loads  are  called  the 
dead  loads  and  include  the  weight  of  the  structural  frame¬ 
work,  walls,  floors,  partitions,  and  roofs.  In  fact,  the  weight 
of  every  piece  of  material  used  in  the  construction  of  the 
building  is  included  in  the  dead  load. 

Before  the  dead  load  can  be  computed,  the  weight  of  vari¬ 
ous  materials  must  be  known,  and  those  in  common  use  in 
building  construction  are  given  in  Tables  I  and  II.  The 
units  in  which  these  weights  are  expressed  are  the  ones  most 
often  employed  in  making  estimates  of  loads  in  engineering 
calculations.  Thus,  Table  I  gives  the  weight,  per  cubic  foot, 
of  the  materials  usually  measured  by  that  unit,  together  with 
the  weight,  per  cubic  inch,  of  a  few  often  measured  in  inches; 
while  Table  II  gives  the  weights  of  such  materials  as  are 
used  in  the  construction  of  floors,  roofs,  ceilings  etc.,  where 
the  quantities  are  generally  expressed  in  square  feet. 

2.  Weight  of  Fireproof  Floors. — If  fireproof  floors 
are  of  standard  construction,  their  weights  may  be  deter¬ 
mined  from  the  weights  given  by  the  manufacturers  of  the 
particular  type  to  be  used.  Where  the  fireproof-floor  system 
is  of  special  construction,  that  is,  different  from  the  standard 
commercial  construction,  a  careful  estimate  of  the  dead  load 

COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  AT  STATIONERS’  HALL,  LONDON 

$4 1 


211—34 


c 


v* 


TABLE  I 

WEIGHT  OF  BUILDING  MATERIALS  (DEAD  LOAD) 


Average  Weight 

Name  of  Material 

Pounds  per 
Cubic  Inch 

Pounds  per 
Cubic  Foot 

Asphalt-pavement  composition . 

130 

Bluestone  . 

160 

Brick,  best  pressed . 

150 

Brick,  common  and  hard . 

125 

Brick,  paving . 

I5° 

Brick,  soft,  inferior . 

100 

Brickwork,  in  lime  mortar  (average)  .... 

120 

Brickwork,  in  cement  mortar  (average)  .  .  . 

130 

Brickwork,  pressed  brick,  thin  joints  .... 

140 

Cement,  Portland,  packed . 

100  to  120 

Cement,  natural,  packed . 

75  to  95 

Concrete,  cinder . 

105 

Concrete,  gravel . 

140 

Concrete,  slag . 

135 

Concrete,  stone . 

140 

Earth,  dry  and  loose . 

72  to  80 

Earth,  dry  and  moderately  rammed . 

90  to  IOO 

Firebrick . 

150 

Granite  . 

165  to  170 

Gravel  .  ' . 

I 17  to  125 

Iron,  cast  . 

.260 

450 

Iron,  wrought . 

.277 

480 

Limestone . 

146  to  168 

Marble . 

168 

Masonry,  squared  granite  or  limestone  .  .  . 

165 

Masonry,  granite  or  limestone  rubble  .... 

15b 

Masonry,  granite  or  limestone  dry  rubble  .  . 

138 

Masonry,  sandstone . 

145 

Mineral  wool  . 

12 

Mortar,  hardened . 

90  to  IOO 

Quicklime,  ground,  loose,  or  small  lumps  .  . 

53 

Quicklime,  ground,  thoroughly  shaken  .  .  . 

75 

Sand,  pure  quartz,  drv . 

90  to  106 

Sandstone,  building,  dry . 

139  to  151 

Slate . . 

160  to  180 

Snow,  fresh  fallen . 

5  to  12 

Steel,  structural . 

.283 

489.6 

Terra  cotta . 

no 

Terra-cotta  masonry  work . 

112 

Tile . 

no  to  120 

2 


TABLE  II 

WEIGHT  OF  BUILDING  MATERIALS  (DEAD  LOAD) 


Name  of  Material 


Corrugated  (2^-inch)  galvanized  iron  • 


Corrugated  galvanized  iron,  No.  20, 

side  lap,  unboarded . *  .  . 

Copper  roofing,  16-ounce,  standing  seam 
Felt  and  asphalt,  without  sheathing  .  .  . 

Glass,  i  inch  thick . 

Hemlock  sheathing,  1  inch  thick  .  .  .  . 

Lead,  about  i  inch  thick . 

Lath-and-plaster  ceiling  (ordinary)  .  .  . 
Mackite,  1  inch  thick,  with  plaster  .  .  . 
Neponset  roofing  felt,  two  layers  .  .  .  . 

Spruce  sheathing,  1  inch  thick . 

i  inch  thick  .  . 


No.  16 . 

No.  18 . 

No.  20 . 

No.  22 . 

No.  24 . 

No.  26' . 

No.  27 . 

No.  28 . 

average  amount  of 


Slate,  single  thickness  < 


inch  thick 
i  inch  thick 
f  inch  thick 
|  inch  thick 
|  inch  thick 
f  inch  thick 


Shingles,  common,  6  in.  X  18  in.,  5  inches  to  weather  . 
Skylight  of  glass,  ^  inch. to  i  inch,  including  frame  .  . 


Slag  roof,  four-ply . 

Steel  roofing,  standing  seam . 

Tiles,  Spanish,  14^  in.  X  10}  in.,  inches  to  weather  .  . 
Tiles,  plain,  ioi  in.  X  6i  in.  X  I  in.,  si  inches  to  weather 

White-pine  sheathing,  1  inch  thick . 

Yellow-pine  sheathing,  1  inch  thick . 

Gravel  roof  and  four-ply  felt . 

Gravel  roof  and  five-ply  felt . 

Roofing,  three-ply  ready  (asphalt,  rubberoid,  etc.)-  .  .  . 

Purlins,  wooden,  with  12-  to  16-foot  span . 

Chestnut  or  maple  sheathing,  1  inch  thick . 

Ash,  hickory,  or  oak  sheathing,  1  inch  thick . 

Sheet  iron,  rg  inch  thick . 

Thatch  . 


Average 

Weight 

Pounds  per 
Square  Foot 


2.91 

2.36 

1.82 

1-54 

1.27 

•99 

•93 

.86 

2i 

ii 

2 

ta 

1 4 

3 

6  to  8 
6  to  8 

10 

j. 

2 

2 

1. 81 
2.71 
3.62 
5-43 
7-25 
9.06 
10.87 

2 

4  to  10 

4 

1 

8i 

18 

3 

4 

6 

.6  to  10 

2 

4 

5 

3 

6-5 


4 


LOADS  IN  STRUCTURES 


§41 


per  square  foot  of  floor  surface  should  be  made.  The  vol¬ 
ume  of  all  materials  that  are  measured  by  the  cubic  inch 
or  the  cubic  foot  should  be  obtained  by  the  rules  and 
methods  set  forth  in  Geometry  and  Mensuration,  and  the  load 
obtained  by  multiplying  by  the  unit  weights  of  the  materials 
found  in  Table  I.  The  area  covered  by  materials  that  are 
measured  by  the  square  foot,  such  as  flooring,  sheathing, 
roof  covering,  etc.,  should  be  computed  and  multiplied  by 
the  weight,  per  square  foot,  as  given  in  Table  II,  to  obtain 
the  load. 

3.  In  making  calculations  for  the  dead  load  of  floors, 
where  the  floor  construction  is  of  uniform  weight  and  thick¬ 
ness  throughout,  as  in  mill  construction,  the  calculations  for 


Layers  of  felt  ^-l"  Yellow  Pine  floorina 


6-0 "Ce liter  to  Center 
Fig.  1 


the  dead  load  can  be  made  directly  for  1  square  foot  of 
floor  surface.  The  size  of  the  girders  or  floorbeams  is 
seldom  known  before  the  dead  load  has  been  determined,  so 
that  it  is  necessary  to  assume  their  size  and  to  add  the  weight 
of  the  assumed  girders  or  beams  in  calculating  the  dead 
load.  When  considering  the  amount  of  dead  weight  sup¬ 
ported  by  a  beam  or  girder,  it  is  customary  to  consider  the 
weight  as  made  up  of  one-half  the  panel  situated  on  either 
side  of  the  beam.  After  the  dead  load  has  been  found  and 
the  size  of  the  girder  accurately  determined,  the  assumed 
weight  of  the  girder  can  be  checked  by  the  actual  weight. 

Example. — In  Fig.  1,  what  is  the  total  dead  load  on  the  girder  Bt 

Solution. — The  weight  of  the  materials  per  square  foot  may  be 
obtained  from  Table  II  and  be  tabulated,  as  follows: 


§41 


LOADS  IN  STRUCTURES 


5 


Yellow-pine  flooring,  1  in.  thick  .  .  . 

4 

lb. 

per 

sq. 

ft. 

Two  layers  of  felt . 

1 

2 

lb. 

per 

sq. 

ft. 

Rough  spruce  flooring,  3  in.  thick  .  . 

6 

lb. 

per 

sq. 

ft. 

Assume  the  weight  of  the  girder  .  .  . 

8 

lb. 

per 

sq. 

ft. 

Total  dead  load  of  floor  surface  .  . 

18* 

lb. 

per 

sq. 

ft. 

The  distance  from  center  to  center  of  girders  being  6  ft.,  and  the 
span  of  the  girders  being  18  ft.,  the  area  of  the  floor  carried  by  each 
girder  is  6  X  18  =  108  sq.  ft.  Then,  108  X  18|  =  1,998  lb.,  which  is 
the  entire  load  on  the  girder  B.  Ans. 

4.  Where  the  section  through  the  floor  shows  irregular¬ 
ities  in  thickness  and,  consequently,  in  volume  and  weight, 
it  is  necessary  to  consider  the  cross-sectional  area  of  a  panel, 
which  is  the  space  between  two  floorbeams.  The  length  of 
section  of  the  floor  considered  is  1  foot,  as  designated  at  xy , 


Fig.  2,  so  that  when  the  entire  weight  of  the  section  has 
been  obtained  the  average  weight  per  square  foot  can  be 
found  by  dividing  by  the  panel  width,  or  the  distance 
between  the  floorbeams. 

Example.— What  is  the  amount  of  dead  load  per  square  foot  of 
floor  surface  on  the  floor  system  shown  in  Fig.  2,  which  consists  of  a 
brick  arch  4  inches  deep,  covered  with  stone  concrete? 

Solution. — The  sectional  area  of  the  brick  arch  is  practically  equal 
to  the  product  of  the  length  of  the  arc  on  the  center  line  a  b  by  the 
thickness  of  the  arch,  which  in  this  instance  is  4  in.  The  length  of  the 
chord  of  the  arc  a  b  is  in.,  while  the  rise  is  5  in.  From  these 
dimensions  the  length  of  the  arc  on  the  center  line  a  b  may  be  found 


6 


LOADS  IN  STRUCTURES 


§41 


by  substituting  in  the  formula  /  = 


4  Vr*  +  4  h2  —  c 


given  in  Geometry 


and  Mensuration ,  in  which  c  equals  the  chord  and  h  the  rise  of  the 
arc.  The  value  of  l  is  found  to  equal 


4  \(47.5  X  47.5)  +  (4  X  5  X  5)-  47.5 


Then,  the  sectional  area  of  the  brick  arch  equals 


=  48.8883  in. 

48.8883  X  4 


144 


=  1.358  sq.  ft.  Since  the  calculation  is  for  a  portion  of  a  floor  sys¬ 
tem  1  ft.  in  length,  the  area  of  the  section  of  the  arch  also  equals, 
numerically,  the  cubical  contents,  so  that  the  weight  of  the  brick  arch 
1  ft.  long  is  equal  to  1.358  multiplied  by  130,  the  weight  per  cubic  foot 
of  brickwork  laid  in  cement  mortar,  obtained  from  Table  I,  or  176.54  lb. 

The  area  of  the  section  of  the  concrete  is  equal  to  the  area  of  a 
rectangle,  in  this  case  7  in.  X  47^  in.,  from  which  must  be  deducted 
the  area  of  the  segment  of  the  circle  included  between  the  arc  ced 
and  the  chord  cd.  In  order  to  obtain  the  area  of  this  segment,  cal¬ 


culate  the  radius  of  the  arc  ced  by  applying  the  formula  r  = 


c2  +  4 
8  h 


r  = 


given  in  Geometry  and  Mensuration.  The  quantities  c  and  h  represent, 
as  before,  the  chord  and  the  rise,  and  are  equal,  respectively,  to 
47.5  in.  and  4.875  in.  Substituting  these  values  in  the  formula, 

(47.5  X  47.5)  +  (4  X  4.875  X  4.875) 

8  X  4.875  °  y  m' 

The  area  of  the  segment  is  equal  to  the  area 
of  the  sector  minus  the  area  of  the  triangle 
formed  by  the  chord  and  the  radii,  or,  as  desig¬ 
nated  in  Fig.  3,  the  area  of  the  shaded  portion 
is  equal  to  the  area  cedo  minus  the  area 
of  the  triangle  cdo.  The  area  of  the  sector 

/  Y 

may  be  found  by  the  formula  a  —  given 

in  Geometry  and  Mensuration ,  in  which  l 
equals  the  length  of  the  arc  and  r  the  radius. 
The  arc  cd  has  a  smaller  rise  than  that  of 
arc  a  b  and  will  therefore  be  shorter.  Its 
length,  found  by  the  formula  just  given,  is 
48.82  in.  Inserting  this  value  and  that  of  the 
radius  in  the  formula, 

48.82  X  60.29 
2 


a  — 


=  1,471.68  sq.  in. 


The  area  of  the  triangle  to  be  deducted 
from  the  sector  is  equal  to  one-half  the  product  of  the  base  and  the  alti¬ 
tude.  From  Figs.  2  and  3,  the  base  equals  47.5  in.  and  the  altitude 


§41 


LOADS  IN  STRUCTURES 


7 


equals  the  radius  minus  the  rise  of  the  arc,  or  60.29  —  4.875  =  55.415  in.; 
consequently,  the  area  of  the  triangle  cdo ,  as  designated  in  Fig.  3,  is 

47^5_X5— 15  =  1,316.11  sq.  in.  Since  the  area  of  the  sector  cedo 


equals  1,471.68  sq.  in.  and  the  triangle  cdo  has  an  area  of  1,316.11  sq. 
in.,  the  area  of  the  segment  ce  d  equals  the  difference  between  these 
quantities,  or  1,471.68  —  1,316.11  =  155.57  sq.  in.  The  area  of  the 
rectangle  from  which  this  area  is  to  be  subtracted  is  7  in.  X  47|  in. 
=  332.5  sq.  in.;  hence,  the  area  of  the  concrete  is  332.5  —  155.57 
=  176.93  sq.  iu.  According  to  Table  I,  the.  weight  of  the  stone  con¬ 
crete  used  is  140  lb.  per  cu.  ft.,  and  as  the  length  of  the  concrete  sec¬ 


tion  is  1  ft.,  its  weight  equals 


176.93 

144 


X  140  =  172  lb. 


The  steel  beam 


shown  in  Fig.  2  weighs  40  lb.  per  lin.  ft.  From  these  calculations, 
the  entire  weight  of  a  panel  section  of  the  floor  system  for  1  ft.  in 
length,  or  per  linear  foot,  may  be  itemized  as  follows: 


Weight  of  brick  arch .  1  7  6.5  4  lb. 

Weight  of  concrete .  1  7  2.0  0  lb. 

Weight  of  steel  beam .  4  0.0  0  lb. 

Total  weight  ....  .  3  8  8.5  4  lb. 


This  amount  is  the  dead  load  on  4  sq.  ft.;  hence,  the  dead  load  per 
square  foot  is  388.54  -s-  4  =  97.14  lb.  Ans. 


5.  Pitch. — Fig.  4  illustrates  a  roof  truss  in  which  a  b, 
or  Z,,  indicates  the  span  and  cd  the  rise.  In  indicating  the 
slope  of  the  roof,  the  angle  x  between  the  rafter  member  ac 


and  the  horizontal  may  be  used,  but  more  frequently  the 
slope  is  indicated  by  the  term  pitch.  As  the  meaning  of 
this  term  is  open  to  several  interpretations,  it  is  important  to 
understand  the  methods  by  which  the  pitch  is  determined. 
The  more  rational  method  would  be  to  divide  the  rise  cd 

7  • 

by  one-half  the  span,  or  — ■  =  — — .  The  quotient,  which  is 

a d  span 

2 


8 


LOADS  IN  STRUCTURES 


41 


the  pitch,  indicates  the  rise  for  each  foot  horizontal.  For 
instance,  a  roof  has  a  rise  of  10  feet  and  a  span  of  80  feet. 

The  pitch  is  nse  =40  =  4,  meaning  that  for  every  4  feet 
span 

horizontal  there  is  a  rise  in  the  rafter  of  1  foot;  or,  when  it  is 
said  that  a  roof  has  a  pitch  of  4,  the  meaning  is  that  for 
every  foot  horizontal  there  is  a  rise  of  i  foot,  or  3  inches. 
The  more  common  method  and  the  one  used  in  this 

rise 

Section  is  to  define  the  pitch  by  the  quotient - .  This 

span 

may  be  expressed  in  the  form  of  a  rule,  as  follows: 

Rule  I. — The  pitch  of  a  roof  is  fo7ind  by  dividing  the  rise  by 
the  span . 

According  to  this  rule,  the  pitch  in  the  preceding  example 
would  be  8"o  =  i.  When  a  roof  is  said  to  be  of  i  pitch,  it 
means  in  this  case  that  in  a  span  of  8  feet  there  is  a  rise 
of  1  foot,  and  in  a  span  of  10  X  8  feet  there  is  a  rise  of 
10  X  1  =  10  feet.  It  is  thus  seen  that  when  using  the  latter 
method,  the  pitch  is  i  of  that  found  by  the  first  method. 
From  this  the  following  rule  may  be  deduced,  applicable  to 
the  pitch  used  in  the  various  Sections: 


Rule  II.  —  To  find  the  rise  per  foot  horizontal  imtltiply  the 
pitch  by  2. 

If  the  pitch  is  known,  the  angle  x  may  be  found  from  the 
rule  of  trigonometry,  by  which 


tan  jtr  = 


cd 
a  d 


rise 

span 


Example  1. — A  roof  has  a  span  of  64 -feet  and  a  rise  of  8  feet. 
Find:  (a)  the  pitch  according  to  rule  I,  and  (b)  the  angle  between  the 
rafters  and  the  horizontal. 


Solution. —  (a)  According  to  rule  I,  the  pitch  is 

rise 


span 


_ 8 _ 1 

~  64  ~  8 


Ans. 


LOADS  IN  STRUCTURES 


9 


(b)  Applying  the  formula, 


tan  x  = 


rise 

span 

9. 


=  A  =  .25 


which  corresponds  to  an  angle  of  14°  2'.  Ans. 

Example  2. — If  the  pitch  of  a  roof  is  what  is  the  rise  of  a  rafter 
for  everv  foot  horizontal? 


Solution. — According  to  rule  II,  the  rise  per  foot  is  twice  the  pitch, 
or  2  X  |  =  i  ft.,  or  4  in.  Ans. 

Another  method  is  to  specify  the  pitch  in  inches.  Thus, 
by  a  6-inch  pitch  is  meant  a  slope  that  has  a  rise  of  6  inches 
to  1  foot  horizontal.  Likewise,  a  3-inch  pitch  is  one  in  which 
there  is  a  3-inch  rise  per  foot  horizontal.  This  method  will 
also  be  found  convenient  at  times. 

.  It  is  therefore  evident  that  the  engineer  should  always 
specify  exactly  what  he  means  by  “pitch”  and  how  it  shall 
be  measured. 


6.  Dead  Load  on  Roof  Trusses. — The  dead  load  also 

includes  the  weight  of  the  roof  covering,  the  sheathing,  and 
\ 

the  roof  trusses.  The  weight  of  the  roof  covering  and  the 
sheathing  may  be  calculated  from  the  unit  weights  given  in 
Table  II.  The  weight  of  the  roof  trusses,  or  principals ,  as 
they  are  termed,  is  not  known  until  these  members  have 
been  designed,  and  must  be  assumed  in  the  original  calcula¬ 
tion.  The  weight  of  roof  trusses  depends  on  the  material 
of  which  they  are  constructed,  the  span,  and  the  distance 
they  are  placed  apart,  and  also  on  the  rise  and  the  type  of 
construction,  though  these  two  latter  factors  are  neglected 
in  the  usual  empirical  formulas. 

The  approximate  weight  of  a  wooden  or  steel  roof  truss 
may  be  determined  by  the  following  formula: 

IV  =  a£>L(l  +  j£j, 

in  which  W  =  approximate  weight  of  truss,  in  pounds; 
a  =  constant — for  wood  .50,  for  steel  .75; 

D  =  distance,  in  feet,  from  center  to  center  of 
trusses; 

L  =  span  of  truss,  in  feet. 


10 


LOADS  IN  STRUCTURES 


§41 


This  formula  may  be  expressed  as  follows: 

Rule. — Multiply  the  constant  {or  the  material  of  which  the 
truss  is  composed  by  the  distance ,  in  feet,  from  center  to  center  of 
trusses  by  the  span  of  the  truss ,  in  feet;  the  product  of  this  result 
and  1  plus  one-tenth  of  the  span  of  the  truss ,  in  feet,  is  the 
approximate  weight  of  the  truss ,  in  pounds. 

7.  It  is  evident  that  the  combined  lengths  of  the  slanting 
sides  of  the  truss  are  greater  than  the  span  of  the  truss;  con¬ 
sequently,  the  length  of  the  panel  supported  by  one  truss  is 
longer  than  the  span.  To  ascertain  the  weight  of  the  frac¬ 
tional  part  of  the  truss  that  is  to  be  added,  per  square  foot 
of  roof  surface,  it  is  necessary  to  calculate  first  the  length  of 
the  slope  and  then  the  area  of  the  roof  surface  supported  by 
each  truss.  Each  of  the  slopes  being  a  hypotenuse  of  a 
right  triangle,  it  is  found  by  trigonometry  that  if  x  is  the 
angle  between  the  rafter  members  and  the  horizontal  and  L 
is  the  span  of  the  truss,  in  feet,  the  combined  lengths  of  the 

two  slopes  are  equal  to  ^ 

cos  x 

The  area  of  the  panel  between  two  trusses  is  therefore 

(1) 

cos  jr 

in  which  D  is  the  distance,  in  feet,  from  center  to  center. 

The  value  of  W ,  as  found  from  the  formula  of  Art.  6, 
must  therefore  be  divided  by  that  of  formula  1  in  order  to 
find  the  approximate  weight  of  the  truss  in  pounds  per  square 
foot  of  roof  surface.  Designating  this  weight  by  w,  then 

W  cos  jt: 

w  = - 

D  L 

Inserting  the  value  of  W,  as  found  by  the  formula  of  Art.  6, 

a  ( 10  +  L)  cos  x 


w  =  a  D  L 


10 


(2 


Formula  2  may  be  stated  in  the  form  of  a  rule  as  follows: 

Rul q.— Multiply  the  constant  by  10  plus  the  span  of  the 
truss ,  in  feet ,  and  by  the  cosine  of  the  angle  that  the  rafter 
member  makes  with  the  horizontal ;  divide  this  product  by  10. 


§41 


LOADS  IN  STRUCTURES 


11 


which  gives  the  approximate  weight  of  the  truss  in  pounds  per 
square  foot  of  roof  surface. 


Example. — Determine  the  weight,  per  square  foot,  that  must  be 
added  to  the  weight  of  a  roof  covering  to  provide  for  the  weight  of  the 
principals,  the  steel  trusses  in  this  case  having  a  span  of  72  feet  and  a 
rise  of  18  feet. 

Solution.— According  to  rules  I  and  II,  Art.  5,  the  roof  has  a 
pitch  of  -y-f  =  -j.  Knowing  the  pitch,  the  angle  may  be  found  directly 

riso 

from  Table  XII,  or  from  the  formula  tan  x  —  — - — -  =  44  =  .5,  corre- 

span  A b 

2~ 


sponding  to  an  angle  ;r  of  26°  34'. 
cos  x  in  formula  2,  Art.  7, 

.75  (10  +  72)  cos  26°  34'  t 


Substituting  the  values  of  a,  L,  and 


.75  X  82  X  .8944 

10. 


5.5  lb.  Ans. 


Table  III  has  been  calculated  from  formula  2.  This 
table  gives  the  weight  that  must  be  added  to  a  square  foot 
of  roof  covering  to  provide  for  the  weight  of  the  principals, 
or  trusses. 


EXAMPLES  FOR  PRACTICE 

1.  A  2"  X  3"  wrought-iron  bar  is  36^  inches  long.  What  is  its 

weight?  Ans.  60.66  lb. 

2.  The  outside  diameter  of  a  cast-iron  column  is  10  inches,  and  the 

thickness  of  the  material  composing  the  column  is  -f-  inch.  What  is 
its  weight  per  foot  of  length?  Ans.  68  lb. 

3.  The  wall  of  a  brick  building,  laid  in  cement  mortar,  is  24  inches 
;  thick,  36  feet  high,  and  100  feet  long;  in  it  are  located  20  window 

openings  2  feet  6  inches  wide  by  6  feet  high.  What  is  the  weight  of 
the  wall?  Ans.  858,000  lb. 

4.  The  roof  of  a  building  is  made  of  No.  20  corrugated  galvanized 

iron,  laid  on  1-inch  spruce  boarding.  What  is  the  weight  of  the  roof 
covering  per  square  foot?  Ans.  3.82  lb. 

5.  What  will  be  the  difference  in  weight  per  square  foot  between 
a  four-ply  slag  roof  laid  on  3-inch,  tongued-and-grooved,  yellow-pine 
planking,  and  a  steel  roof,  standing  seam,  laid  on  2-inch  hemlock  sheath¬ 
ing  that  is  covered  with  two  layers  of  Neponset  roofing  felt?  Ans.  8^  lb. 

6.  The  span  of  a  steel  roof  truss  is  40  feet  and  its  rise  is  10  feet. 

Referring  to  Table  III,  what  weight  per  square  foot  of  roof  surface 
should  be  assumed  so  as  to  allow  for  the  weight  of  the  principal,  or 
roof  truss?  Ans.  3.35  lb. 


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12 


LOADS  IN  STRUCTURES 


13 


LIVE  LOAD 

8.  Besides  the  dead  load,  which  includes  the  weight  of  all 
the  material  used  in  the  structure  itself,  there  is  a  load  called 
the  live  load.  The  live  load  comprises  people  in  the  build¬ 
ing,  furniture,  movable  stocks  of  goods,  small  safes,  and 
varying  weights  of  any  character.  Large  safes  and  extremely 
heavy  machinery  require  some  special  provision,  which  is 
usually  embodied  in  the  construction.  Table  IV  gives  the 
live  loads  per  square  foot  recommended  as  good  practice  in 
conservative  building  construction. 

TABLE  IV 

LIVE  LOADS  PER  SQUARE  FOOT  IN  BUILDINGS 


Character  of  Building 

Pounds 

Dwellings . 

Offices . 

Hotels  and  apartment  houses . 

Theaters . 

Churches . 

Ballrooms  and  drill  halls . 

Factories . 

Warehouses . 

70 

70 

70 

120 

120 

120 

from1  150  up 
from  150  to  250  up 

The  load  of  70  pounds  will  probably  never  be  realized  in 
dwellings;  but  inasmuch  as  a  city  house  may  at  times  be 
used  for  some  purpose  other  than  that  of  a  dwelling,  it  is  not 
generally  advisable  to  use  a  lighter  load.  In  the  case  of  a 

country  house,  a  hotel,  or  a  building  of  like  character,  where 
economy  demands  it  and  where  the  building  is  likely  to  be 
used  indefinitely  for  some  fixed  purpose,  a  live  load  of 
40  pounds  per  square  foot  of  floor  surface  is  ample  for 
all  rooms  not  used  for  public  assembly. 

For  assembly  rooms,  a  live  load  of  100  pounds  will  be 
sufficient,  experience  having  demonstrated  that  a  floor  is  not 
liable  to  be  loaded  with  a  greater  weight  than  this.  If  the 


14 


LOADS  IN  STRUCTURES 


41 


desks  and  chairs  are  fixed,  as  in  a  schoolroom  or  a  church,  a 
live  load  of  more  than  from  40  to  50  pounds  will  never  be 
attained.  Retail  stores  should  have  floors  proportioned  for 
a  live  load  of  100  pounds  and  upwards.  Wholesale  stores, 
machine  shops,  etc.  should  have  the  floors  proportioned  for  a 
live  load  of  not  less  than  150  pounds  per  square  foot.  The 
floors  of  printing  houses  and  binderies,  especially  where  the 
accumulation  of  heavy  stock,  such  as  bound  volumes  and 
calendered  paper,  is  likely  to  occur,  should  be  proportioned  for 
a  live  load  of  at  least  250  pounds  per  square  foot.  Special 
provision  should  be  made  in  floor  systems  for  heavy  presses, 
trimmers,  and  cutters,  and  the  beams  should  be  proportioned 
for  twice  the  static  load  likely  to  occur  from  such  machines. 

The  static  load  in  factories  seldom  exceeds  from  40  to  50 
pounds  per  square  foot  of  floor  surface;  therefore,  in  the 
majority  of  cases,  a  live  load  of  100  pounds,  including  the 
effects  of  vibrations  due  to  moving  machinery,  is  ample. 
The  conservative  rule  is,  in  general,  to  assume  loads  not 
less  than  those  just  given,  and  to  proportion  the  beams  so 
as  to  avoid  excessive  deflection.  Stiffness  is  as  important 
a  factor  as  strength. 

9.  Live  Loads  on  Warehouse  Floors. — In  the  design 
Af  warehouse  floors,  the  character  of  the  material  to  be 
stored  should  be  considered  and  data  in  regard  to  the  manner 
of  storing,  the  bulk  of  the  packages,  and  the  weight  of  the 
load  per  square  foot  should  be  obtained.  With  the  view  of 
furnishing  reliable  data  to  manufacturers,  architects,  and 
engineers,  the  Boston  Manufacturers’  Mutual  Fire  Insurance 
Company  has  prepared  the  table  designated  as  Table  V. 
This  table  gives  the  space  that  the  merchandise  occupies 
and  the  greatest  possible  loads  that  can  be  placed  on  ware¬ 
house  floors  with  the  usual  system  of  loading.  Where  the 
floor  space  and  the  cubical  contents  of  the  load  are  given 
in  the  table,  the  height  of  the  load  above  the  finished  floor 
may  be  obtained  by  dividing  the  volume  of  the  load  by  the 
floor  area  that  is  covered.  For  instance,  the  floor  space 
occupied  by  a  bale  of  white  linen  rags  is  8.5  square  feet, 


§41 


LOADS  IN  STRUCTURES 


15 


and  the  cubical  contents  is  39.5  cubic  feet;  then  the  height 
of  the  loading  is  39.5  4-  8.5  =  4.65  feet.  It  is  hardly  pos¬ 
sible,  in  the  absence  of  hoists,  to  place  such  materials  on  the 
floor  more  than  one  bale  in  thickness,  and  the  same  thing 
applies  to  merchandise  in  barrels  on  the  side  and  end. 

The  building  ordinances  of  the  principal  American  cities 
are  particularly  emphatic  with  reference  to  warehouse  floors. 
For  instance,  the  building  laws  of  Greater  New  York  stipu¬ 
late  that,  “in  all  warehouses,  storehouses,  factories,  work¬ 
shops,  and  stores  where  heavy  materials  are  kept  or  stored, 
or  machinery  introduced,  the  weight  that  each  floor  will 
safely  sustain  on  each  superficial  foot  thereof,  or  on  each 
.  varying  part  of  such  floor,  shall  be  estimated  by  the  owner  or 
occupant,  or  by  a  competent  person  employed  by  the  owner 
or  occupant.  Such  estimate  shall  be  reduced  to  writing  or 
printed  forms  furnished  by  the  Department  of  Buildings,  sta¬ 
ting  the  material,  size,  distance  apart,  and  span  of  beams  and 
girders,  posts  or  columns  to  support  floors,  and  its  correct¬ 
ness  shall  be  sworn  to  by  the  person  making  the  same,  and 
it  shall  thereupon  be  filed  in  the  office  of  the  Department  of 
Buildings.  But  if  the  commissioners  of  buildings  shall  have 
cause  to  doubt  the  correctness  of  said  estimate,  they  are 
empowered  to  revise  and  correct  the  same,  and  for  the  pur¬ 
pose  of  such  revision  the  officers  and  employes  of  the 
Department  of  Buildings  may  enter  any  building  and  remove 
so  much  of  any  floor  or  any  portion  thereof  as  may  be 
required  to  make  necessary  measurements  and  examination. 
When  the  correct  estimate  of  the  weight  that  the  floors  in 
any  such  buildings  will  safely  sustain  has  been  ascertained  as 
herein  provided,  the  Department  of  Buildings  shall  approve 
the  same,  and  thereupon  the  owner  or  occupant  of  said  build¬ 
ing,  or  of  any  portion  thereof,  shall  post  a  copy  of  such 
approved  estimate  in  a  conspicuous  place  on  .each  story  or 
varying  parts  of  each  story  of  the  building  to  which  it 
relates.  *  *  *  No  person  shall  place  or  cause  or  permit 
to  be  placed  on  any  floor  of  any  building  any  greater  load 
than  the  safe  load  thereof,  as  correctly  estimated  and 
ascertained  as  herein  provided.” 


TABLE  V 


WEIGHTS  OF  MERCHANDISE,  IN  BULK,  FOR  CALCULATING 

LIVE  LOADS 


Materials 

Measurements 

Approximate  Weights 

Floor  Area 

Square 

Feet 

Contents 

Cubic 

Feet 

Total 

Pounds 

Pounds  per 
Square 
Foot 

Pounds  pc 
Cubic 
Foot 

Cotton ,  etc.: 

Bale  of  commercial  cotton  . 

8.1 

44.2 

5T5 

64 

12 

Bale  of  compressed  cotton  . 

4.1 

21.6 

550 

134 

25 

Bale  of  American  Cotton  Co. 

4.0 

1 1 .0 

263 

66 

24 

Bale  of  Planters  Compress 

Co . 

2-3 

7.2 

254 

1 10 

35 

Bale  of  jute . 

2.4 

9.9 

300 

125 

30 

Bale  of  jute  lashings  .... 

2.6 

10.5 

450 

172 

43 

Bale  of  manila . 

3-2 

10.9 

280 

88 

26 

Bale  of  hemp . 

8.7 

34-7 

700 

81 

20 

Bale  of  sisal . 

5-3 

17.0 

400 

75 

24 

Cotton  Goods: 

Bale  of  unbleached  jeans 

4.0 

12.5 

300 

75 

24 

Piece  of  duck . 

1. 1 

2.3 

7  5 

68 

33 

Bale  of  brown  sheetings  .  . 

3-6 

10. 1 

235 

65 

23 

Case  of  bleached  sheetings  . 

4.8 

11. 4 

330 

69 

29 

Case  of  quilts . 

7.2 

19.0 

295 

4i 

16 

Bale  of  print  cloths  .... 

4.0 

9-3 

175 

44 

19 

Case  of  prints . 

4-5 

13-4 

420 

93 

3i 

Bale  of  tickings . 

3-3 

8.8 

325 

99 

37 

Burlaps . 

130 

30 

Jute  bagging . 

1.4 

5-3 

100 

7i 

19 

Grain: 

Wheat  in  bags . 

4.2 

4.2 

165 

39 

39 

Flour  in  barrels  on  side  .  . 

4.10 

5-40 

218 

53 

40 

Flour  in  barrels  on  end  .  . 

3.10 

7.10 

218 

70 

3i 

Corn  in  bags . 

3.60 

3.60 

1 12 

3r 

3i 

Corn  meal  in  barrels  .... 

3-70 

5-9° 

218 

59 

37 

Oats  in  bags . 

3-30 

3.60 

96 

29 

27 

Bale  of  clover  hay . 

5.00 

20.00 

284 

57 

14 

Clover  hay,  derrick  com- 

.  V 

pressed . 

i-75 

5-25 

125 

71 

24 

Straw  ...  . 

i-75 

5-25 

100 

57 

19 

Tow . 

i-75 

5-25 

150 

86 

29 

Excelsior . 

i-75 

5-25 

100 

57 

19 

Rags  in  Bales: 

White  linen . 

8.50 

39-50 

910 

107 

23 

White  cotton . 

9.20 

40.00 

7 1 5 

78 

18 

Brown  cotton . 

7.60 

30.00 

442 

58 

15 

Paper  shavings . 

7-50 

34.00 

507 

68 

15 

Sacking . 

16.00 

65.00 

450 

28 

7 

Woolen . 

7-50 

30.00 

600 

80 

20 

Jute  butts . 

2.80 

1 1. 00 

400 

M3 

36 

Hoot: 

Bale,  East  India . 

3-o 

12 

340 

113 

28 

Bale,  Australian  .... 

5-8 

26 

385 

66 

15 

10 


TA BIjE  V—  ( Continued ) 


Materials 

Measurements 

Approximate  Weights 

Floor  Area 

Square 

Feet 

Contents 

Cubic 

Feet 

Total 

Pounds 

Pounds  per 
Square 
Foot 

Pounds  per 
Cubic 
Foot 

Wool: 

Bale,  South  American  .  .  . 

7.0 

34-0 

1,000 

143 

29 

Bale,  Oregon . 

6.9 

33-o 

482 

70 

15 

Bale,  California . 

7-5 

33-0 

550 

73 

17 

Bag  of  wool . 

5-0 

30.0 

200 

40 

7 

Sack  of  scoured  wool  .  .  . 

5 

Woolen  Goods: 

Case  of  flannels . 

5-5 

12.7 

220 

40 

17 

Case  of  flannels,  heavy  .  . 

7-i 

152 

330 

46 

22 

Case  of  dress  goods  .... 

5-5 

22.0 

460 

84 

21 

Case  of  cassimeres . 

10.5 

28.0 

550 

52 

20 

Case  of  underwear . 

7-3 

21.0 

350 

48 

17 

Case  of  blankets . 

10.3 

35-o 

450 

44 

13 

Case  of  horse  blankets  .  .  . 

4.0 

14.0 

250 

63 

18 

Miscellaneous: 

• 

Box  of  tin . 

2.7 

•  5 

139 

5i 

278 

Crate  of  crockery . 

9.9 

39-6 

I  ,600 

]  62 

40 

Cask  of  crockery . 

13-4 

42.5 

600 

45 

14 

Bale  of  leather . 

7-3 

12.2 

190 

26 

16 

Bale  of  goat  skins . 

1 1.2 

16.7 

300 

27 

18 

Bale  of  raw  hides . 

6.0 

30.0 

400 

67 

13 

Bale  of  raw  hides,  com- 

pressed . 

6.0 

30.0 

700 

ii7 

23 

Bale  of  sole  leather  .... 

12.6 

8.9 

200 

16 

22 

Barrel  of  granulated  sugar 

3-0 

7-5 

317 

106 

42 

Barrel  of  brown  sugar  .  .  . 

3-o 

7-5 

339 

113 

45 

Hogshead  of  bleaching 

powder . 

11. 8 

39-2 

1,200 

102 

3i 

Hogshead  of  soda  ash  .  .  . 

10.8 

29.2 

1,800 

167 

62 

Box  of  indigo . 

3-0 

9.0 

385 

128 

43 

Box  of  sumac . 

1.6 

4.1 

160 

100 

39 

Caustic  soda  in  iron  drum  . 

4-3 

6.8 

600 

140 

88 

Barrel  of  starch . 

3-o 

10.5 

250 

83 

24 

Barrel  of  pearl  alum  .... 

3-o 

10.5 

350 

117 

33 

Box  of  extract  logwood  .  . 

1. 1 

.8 

57 

52 

7i 

Barrel  of  lime . 

3-6 

4-5 

225 

63 

50 

Barrel  of  Portland  cement  . 

3-8 

376 

100  to  120 

Barrel  of  natural  cement  .  . 

3-8 

282 

75  to  95 

Barrel  of  slag  cement  .  .  . 

3-8 

330 

80  to  100 

Barrel  of  English  Portland 

cement . 

3-8 

5-5 

400 

105 

73 

Barrel  of  plaster . 

3-7 

6.1 

325 

88 

53 

Barrel  of  rosin . 

3-o 

9.0 

430 

143 

48 

Barrel  of  lard  oil . 

4-3 

12.3 

422 

98 

34 

Books  in  library . 

30 

Crowd  of  men . 

134  to  157 

17 


211—35 


18  LOADS  IN  STRUCTURES  §41 

TABLE  YI 

AVERAGE  WEIGHTS  OF  MISCELLANEOUS  MATERIALS 


Name  of  Material 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Name  of  Material 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Acid,  acetic . 

66 

Clay,  potters’,  dry  .  .  . 

1 19 

Acid,  fluoric . 

94 

Clinker . 

85 

Acid,  muriatic  (hydro- 

Coal,  anthracite,  broken 

54 

chloric) . 

75 

Coal,  anthracite,  mod- 

Acid,  nitric . 

76 

erately  shaken  .  .  . 

58 

Acid,  phosphoric  .  .  . 

97 

Coal,  anthracite,  solid  . 

93 

Acid,  sulphuric  .... 

115 

Coal,  bituminous, 

Alabaster,  white  .... 

171 

broken,  loose  .... 

54 

Alabaster,  yellow  .  .  \ 

169 

Coal,  bituminous, 

Alcohol,  commercial  .  . 

52 

slaked . 

53 

Alcohol,  grain . 

49.6 

Coal,  bituminous,  solid 

84 

Alcohol,  wood . 

49.9 

Coal,  cannel,  solid  .  .  . 

79 

Aluminum  . 

167 

Coke,  loose . 

23  to  32 

Ammonia,  28  percent.  . 

56 

Copper,  cast . 

552 

Antimony . 

418 

Cork . 

15 

Asbestos,  starry  .... 

192 

Corundum . 

244 

Ashes . 

40 

Cotton  yarn,  in  skeins  . 

11 

Asphalt,  pure . 

80 

Earth,  common  loam, 

Basalt . 

181 

loose  . 

72  to  80 

Beer,  lager . 

65 

Earth,  common  loam, 

Bismuth  . 

613 

shaken  . 

82  to  92 

Brass . 

523 

Earth,  common  loam, 

Bronze . 

546 

rammed  moderately  . 

90  to  IOO 

Cement,  Portland, 

Earth,  like  soft,  flowing 

packed  . 

100  to  120 

mud . 

108 

Cement,  Portland,  loose 

70  to  90 

Earth,  like  dense  mud 

125 

Cement,  natural, 

Emery . 

250 

packed  . 

75  to  95 

Ether,  sulphuric  .  .  . 

45 

Cement,  natural,  loose 

45  to  65 

Feldspar . 

166 

Cement,  slag,  packed  . 

80  to  100 

Flint . 

162 

Cement,  slag,  loose  .  . 

55  to  75 

Glass,  common  .... 

156  to  172 

Chalk . 

156 

Glass,  flint . 

180  to  196 

Charcoal  from  birch  .  . 

34 

Gneiss,  common  .  .  . 

168 

Charcoal  from  fir  .  .  . 

28 

Gneiss,  in  loose  piles  .  . 

96 

Charcoal  from  oak  .  .  . 

k 

21 

Gold,  cast,  24  carat  .  . 

1,204 

Charcoal  from  pine  .  . 

18 

;  Gold,  pure,  hammered  . 

1,217 

Chrome  ore  dust,  well 

Grindstone . 

134 

shaken  . 

160 

Gun  metal . 

528 

Clay,  ordinary  .... 

120  to  150 
\ 

Gunpowder,  loose  .  .  . 

56 

§41  LOADS  IN  STRUCTURES  19 

TABLE  VI — {Continued) 


Name  of  Material 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Name  of  Material 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Gunpowder,  shaken  .  . 

63 

Papei1,  wrapping  .  .  . 

IO 

Gunpowder,  solid  .  .  . 

105 

Paper,  writing  .... 

64 

Gutta  percha . 

6l 

Paving  stone . 

1 5° 

Gypsum . 

M3 

Peat,  dry,  compressed  . 

20  to  30 

Hematite  ore . 

306 

Petroleum . 

55 

Hornblende . 

203 

Pitch . 

72 

Ice . 

1 

57 

Plaster  of  Paris,  cast  .  . 

80 

India  rubber . 

58 

Platinum  ...... 

L342 

Iron,  cast . 

450 

Plumbago . 

140 

Iron,  wrought . 

480 

Porphyry . 

170 

Isinglass . 

70 

Pumice  stone . 

57 

Ivory  . 

114 

Quartz,  common  pure  . 

165 

Lead,  commercial  cast  . 

712 

Rosin . 

69 

Leather,  sole,  in  piles  . 

17 

Rope . 

42 

Magnesia,  carbonate  .  . 

150 

Rottenstone  .;.... 

124 

Magnesite,  calcined  .  . 

no 

Saltpeter . 

131 

Magnesium . 

109 

Salt,  coarse . 

45 

Manganese . 

499 

Salt,  West  India,  well- 

Mastic  . 

67 

dried . 

74 

Mercury,  at  6o°  F.  .  .  . 

846 

Sand . 

90  to  106 

Mica . 

183 

Silver  . 

655 

Millstone . 

155 

Slate  . 

174 

Naphtha . 

53 

Soil,  common . 

124 

Nickel  . 

548 

Soapstone . 

170 

Niter . 

119 

Spelter,  or  zinc  .... 

437 

Oil,  linseed . 

59 

Spermaceti . 

59 

Oil,  olive . 

57 

Steel . 

490 

Oil,  turpentine  .... 

54 

Sugar  . 

100 

Oil,  whale . 

58 

Sulphur . 

125 

Ore,  hard  iron  (mag- 

Talc,  block . 

181 

netite)  . 

312 

Tallow,  sheep  or  ox  .  . 

58 

Ore,  soft  iron  (hematite) 

306 

Tar  . 

63 

Paper,  calendered,  book 

50 

Tin . 

458 

Paper,  leather-board  .  . 

59 

Trap . 

170 

Paper,  manila . 

37 

Turf,  or  peat . 

20  to  30 

Paper,  news . 

38 

Vinegar  . 

68 

Paper,  strawboard  .  . 

33 

Whalebone . 

81 

Paper,  supercalendered, 

Wines . 

62 

book . 

69 

Zinc . 

437 

20 


LOADS  IN  STRUCTURES 


§41 


TABLE  VII 

AVERAGE  WEIGHTS  OF  FARM  PRODUCTS 


Name  of  Material 

Weight  per 
Cubic  Foot 

Pounds 

Name  of  Material 

Weight  per 
Cubic  Foot 

Pounds 

Apples . 

38 

Fat  of  mutton  .... 

58 

Apples,  dried . 

20 

Flaxseed  (linseed)  .  .  . 

45 

Apple  seeds . 

32 

Gooseberries . 

34 

Barley  . 

38 

Grapes  with  stems  .  .  . 

38 

Beans,  white . 

48 

Guavas . 

43 

Beans,  castor,  shelled  . 

37 

Hay,  alfalfa,  in  bales  . 

12.51014.3 

Beeswax  . 

61 

Hay,  alfalfa,  in  rectan- 

Beets . 

44 

gular  double-com- 

Beggarweed  seeds  .  .  . 

50 

pressed  bales  .... 

23.53 

Blackberries . 

32 

Hay,  alfalfa,  in  cylin- 

Blueberries . 

34 

drical  double-com- 

Blue-grass  seeds  .... 

11 

pressed  bales  .... 

36.36 

Bran . 

16 

Hay,  clover,  in  bales  . 

14 

Brorae  grass . 

1 1 

Hay,  clover, compressed 

24 

Broom-corn  seed  .  .  . 

30 

Hay,  clover,  in  mow 

4.6 

Buckwheat . 

39 

Hair,  plastering  .... 

6 

Butter  . 

59 

Hemp  seed . 

35 

Cabbage  . 

40 

Hickory  nuts . 

40 

Canary  seed . 

48 

Hominy . 

49 

Cantaloupe,  melon  .  .  . 

40 

Horseradish . 

40 

Carrots . 

40 

Hungarian  grass  seed  . 

39 

Cheese . 

30 

Indian  corn,  or  maize  . 

45 

Cherries . 

40 

Italian  rye-grass  seed  . 

16 

Chestnuts . 

43 

Johnson  grass  .... 

22 

Chufa . 

43 

Kaffir  corn . 

45 

Cider  . 

64 

Kale . 

24 

Clover  seed . 

48 

Land  plaster . 

80 

Corn  on  the  cob,  husked 

56 

Lard . 

59 

Corn  on  the  cob,  un- 

Lime . 

64 

husked  . 

58 

Malt . 

27 

Corn,  shelled . 

45 

Meal . 

37 

Corn  meal,  bolted  .  .  . 

37 

Middlings,  coarse  .  .  . 

38 

Corn  meal,  unbolted  .  . 

38 

Middlings,  fine  .... 

32 

Cottonseed . 

25 

Milk . 

65 

Cranberries . 

29 

Millet . 

40 

Currants . 

32 

Millet,  Japanese  barn- 

Fat  of  beef . 

58 

yard . 

28 

Fat  of  hogs . . 

59 

Mustard . 

24 

§41 


LOADS  IN  STRUCTURES 


21 


TABLE  VII — [Continued) 


Name  of  Material 

Weight  per 
Cubic  F'oot 

Pounds 

Name  of  Material 

Weight  per 
Cubic  Foot 

Pounds 

Oats . 

26 

Redtop . 

II 

Onions . 

45 

Rhubarb . 

40 

Orchard-grass  seed  .  . 

1 1 

Rice  corn  . 

45 

Osage-orange  seed  .  .  . 

26 

Rice,  rough . 

35 

Parsnips . 

38 

Rutabagas . 

45 

Peaches  . . 

40 

Rye  . 

45 

Peaches,  dried  and 

Rye  meal . 

40 

peeled  . 

26 

Sage . 

3 

Peanuts . 

18 

Sorghum  seed  .... 

37 

Pears . 

39 

Spelt,  or  speltz  .... 

34 

Peas . 

48 

Spinach . 

24 

Plums . 

42 

Straw . 

19 

Plums,  dried . 

22 

Strawberries . 

32 

Popcorn  . 

56 

Sugar-cane  seed  .  .  . 

•46 

Popcorn,  on  the  cob  .  . 

34 

Tares . 

49 

Potatoes,  white  .... 

48 

Timothy  seed . 

36 

Potatoes,  sweet  .... 

4i 

Tomatoes . 

44 

Prunes,  dried . 

22 

Turnips  . 

44 

Prunes,  green . 

36 

Velvet-grass  seed  .  .  . 

6 

Ouinces . 

38 

Walnuts . 

40 

Rape  seed . 

40 

Wheat . 

48 

Raspberries . 

32 

10.  Additional  information  about  weights  of  materials 
is  found  in  Tables  VI,  VII,  VIII,  and  IX.  Table  VI  gives 
the  average  weight  per  cubic  foot  of  miscellaneous  materials 
likely  to  be  stored;  Table  VII,  the  average  weights  of  farm 
products;  Table  VIII,  the  average  weight  per  cubic  foot  of 
various  native  and  foreign  woods;  and  Table  IX  deals  solely 
with  woods  found  in  the  Philippine  Islands.  The  weight  of 
woods  depends  very  much  on  the  amount  of  moisture  they 
contain.  The  weights  given  in  Tables  VIII  and  IX  are  for 
commercially  dry,  or  well-seasoned,  wood,  and  not  for 
green  wood. 


22 


LOADS  IN  STRUCTURES 


§41 


TABLE  VIII 


WEIGHT  OF 

WOODS, 

COMMERCIALLY  DRY 

Name  of  Tree 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Name  of  Tree 

Average 
Weight  per 
Cubic  Foot 
Pounds 

Alder . 

42 

Cedar,  juniper  .... 

% 

35 

Apple . 

47 

Cedar,  Palestine  .  .  . 

38 

Arbor  vitae . 

19 

Cedar,  Port  Oxford  .  . 

28 

Ash,  black . 

39 

Cedar,  red . 

30 

Ash,  blue . 

44 

Cedar,  white,  or  post  . 

23 

Ash,  screen . 

39 

Cedar,  white  (arbor  vitae) 

19 

Ash,  Oregon . 

35 

Cedar,  wild . 

37 

Ash,  red . 

38 

Cedar,  yellow . 

29 

Ash,  white . 

39 

Cherry,  wild  black  .  .  . 

36 

Aspen  . 

27 

Chestnut . 

28 

Bamboo . ' .  . 

22 

Chinkapin . 

36 

Basswood . 

28 

Citron . 

45 

Bay  tree . 

5i 

Cocoa  wood  . 

65 

Beech . 

42 

Cocobolo . 

55 

Bethabara . 

76 

Cottonwood  . 

24 

Birch,  paper,  or  white  . 

37 

Cottonwood,  black  .  . 

*  23 

Birch,  red . 

35 

Cucumber  tree  .... 

29 

Birch,  sweet . 

47 

Cypress,  bald . 

29 

Birch,  yellow . 

40 

Cypress,  Spanish  .  .  . 

40 

Blue  beech  (ironwood)  . 

45 

Dagame . 

56 

Blue  gum  (fever  tree)  . 

43  to  69 

Dogwood . 

50 

Box  elder,  or  ash-leaved 

Ebony . 

76 

maple . 

26 

Elder  tree  . 

43 

Boxwood,  Brazilian,  red 

64 

Elm,  cork . 

45 

Boxwood,  Dutch  .  .  .  . 

83 

Elm,  slippery . 

43 

Boxwood,  French  .  .  . 

57 

Elm,  white . 

34 

Buckeye,  Ohio . 

28 

Elm,  wing . 

46 

Buckeye,  sweet  .... 

27 

Filbert  tree . 

38 

Butternut . 

25 

Fir,  balsam . 

23 

Buttonwood,  or  syca- 

Fir.  great  silver  .... 

22 

more . 

35 

Fir,  red,  or  California  . 

29 

Catalpa,  or  Indian  bean 

27 

Fir,  red,  or  noble  .  .  . 

28 

Catalpa,  hardy  .... 

25 

Fir,  white . 

22 

Cedar,  California  white 

25 

Greenheart . 

72 

Cedar,  canoe . 

23 

Gum,  cotton . 

32’ 

Cedar,  incense . 

25 

Gum,  sour . 

39 

Cedar,  Indian . 

82 

Gum,  sweet . 

37 

§41 


LOADS  IN  STRUCTURES 


23 


TABLE  VIII-  ( Continued ) 


Name  of  Tree 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Name  of  Tree 

# 

Average 
Weight  per 
Cubic  Foot 
Pounds 

Hackmatack  (American 

• 

Maple,  Oregon  .... 

30 

larch) . 

33 

Maple,  red . 

38 

Hazel . 

38 

Maple,  silver,  or  soft  . 

32 

Hemlock . 

26 

Maple,  sugar,  or  hard  . 

43 

Hemlock,  Western  .  .  . 

28 

Mastic  tree . 

53 

Hickory,  mocker  nut  . 

53 

Medlar . 

59 

Hickory,  pecan  .... 

49  . 

Mesquit  . 

47 

Hickory,  pignut  .... 

5b 

Missel  tree . 

59 

Hickory,  shagbark,  or 

Mulberry,  red  or  black 

36 

shellbark . 

5i 

Oak,  black . 

45 

Holly . 

36 

Oak,  bur . 

46 

Hornbeam  . 

47 

Oak,  chestnut  .... 

46 

Ironwood,  or  blue  beech 

45 

Oak,  cow . 

46 

Iron  wood,  or  hop  horn- 

Oak,  English . 

5i 

beam . 

5i 

Oak,  live,  California 

5i 

Jarrah  . 

65 

Oak,  live  (found  in  the 

Joshua  tree . 

23 

Southern  States)  .  . 

59 

Jasmine,  Spanish  .  .  . 

48 

Oak,  pin . 

43 

Jucaro  Prieto . 

67 

Oak,  post  . 

50 

Juneberry . 

54 

Oak,  red . 

45 

Karri . 

63 

Oak,  Spanish . 

43 

Kranji  . 

64 

Oak,  white  (North- 

Larch . 

38 

Central  and  Eastern 

Larch,  tamarack  .  .  . 

46 

United  States)  .  .  . 

50 

Laurel,  California  .  .  . 

40 

Oak,  white  (Pacific 

Laurel,  Madrona  .  .  . 

43 

Coast  from  British 

Lemon . 

45 

Columbia  into  Cali- 

Lignum  vitae . 

83 

fornia)  . 

46 

Linden . 

38 

Orange,  Osage  .... 

48 

Locust,  black,  or  yellow 

45 

Orange  tree  . 

44 

Locust,  honey . 

42 

Paddlewood . 

52 

Logwood  . 

58 

Palm ,  Washington  .  . 

32 

Madrona . 

43 

Palmetto,  cabbage  .  . 

27 

Mahoe . 

4i 

Pear . 

4i 

Mahogany  . 

45 

Persimmon . 

49 

Mahogany,  Mexican  .  . 

32 

Pine,  bull . 

29 

Mahogany,  Spanish  .  . 

53 

Pine,  Cuban . 

39 

Mahogany,  white  .  .  . 

33 

Pine,  Kauri . 

33 

24 


LOADS  IN  STRUCTURES 


41 


TABLE  VIII—  ( Continued ) 


Name  of  Tree 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Name  of  Tree 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Pine,  loblolly . 

33 

Spruce,  black . 

28 

Pine,  long-leaf,  or  Geor- 

Spruce,  Douglas  .  .  . 

32 

gia . 

33 

Spruce,  Norway  .  .  . 

29 

Pine,  northern . 

34 

Spruce,  single  (balsam 

Pine,  Norway . 

3i 

fir)  .  .  .  ,  . 

23 

Pine,  Oregon . 

32 

Spruce,  Sitka . 

26 

Pine,  pitch . 

32 

Spruce,  white  (Northern 

Pine,  short-leaf,  or  Car- 

United  States)  .  .  . 

25 

olina . 

32 

Spruce,  white  (Rocky 

Pine,  sugar . 

\  22 

Mountainsand  British 

Pine,  white  (North-Cen- 

Columbia) . 

21 

tral  and  Northeastern 

Sycamore,  or  button- 

States)  . 

24 

wood . 

35 

Pine,  white  (Pacific 

Sycamore,  California  . 

30 

States  and  British 

Tamarack . 

3S 

Columbia)  . 

24 

Teak . 

50 

Pine,  white  (Rocky 

Tooart . 

67 

Mountains) . 

27 

Tulip  tree . 

26 

Pingow . 

47 

Tulip  wood . 

61 

Plum  tree . 

49 

Vine  tree . 

83 

Pockwood . 

8i 

Walnut,  black  .... 

38 

Poplar,  or  large-tooth 

Walnut,  Circassian  .  . 

35 

aspen  . 

28 

Walnut,  English  .  .  . 

36 

Poplar,  yellow,  or  tulip 

Walnut,  Italian  .... 

42 

tree . 

26 

Walnut,  Persian  .  .  . 

36 

Pomegranate  tree  .  .  . 

85 

Walnut,  white  .... 

25 

Quebracho . 

82 

Wasahba . 

76 

Quince  tree . 

44 

Whitewood . 

26 

Redwood . 

26 

Willow,  black . 

27 

Roller  wood . 

52 

Yarura . 

52 

Rosewood . 

68 

Yew,  Dutch . 

49 

Sassafras . 

3i 

Yew,  Spanish . 

50 

Shadblow . 

54 

Yucca,  or  joshua  tree  . 

23 

Shadbush  . 

54 

41 


LOADS  IN  STRUCTURES 


25 


TABLE  IX 

WEIGHT  OF  PHILIPPINE  WOODS 


Name  of  Tree 

Average 
Weight  per 
Cubic  Foot 
Pounds 

Name  of  Tree 

Average 
Weight  per 
Cubic  Foot 

Pounds 

Acle  . 

37 

Liusin . 

44 

Amuguis . 

43 

Lumbayao . 

35 

Apitong . 

4i 

Macaasin . 

44 

Aranga  . 

54 

Malasantol . 

40 

Balacat . 

33 

Malugay . 

40 

Balacbacan . 

34 

Mayapis . 

25 

Bansalaguin . 

53 

Molave . 

49 

Banuyo  . 

33 

Narra . 

36 

Batitinan . 

49 

Palo  Maria . 

39 

Betis  . 

49 

Sacat . 

37 

Calantas . 

27 

Sasalit . 

55 

Dungon  . 

49 

Supa . 

45 

Guijo . 

43 

Tanguile . 

30 

Ipil . 

47 

Tindalo  . 

48 

Lauan  . 

29 

Yacal . 

52 

Example. — What  will  be  the  entire  live  load  coming  on  a  large 
girder  supporting  a  portion  of  a  church  floor  if  the  floor  area  to  be 
supported  is  600  square  feet? 

Solution. — From  the  list  given  in  Table  IV,  120  lb.  is  usually  con¬ 
sidered  safe  for  a  live  load  in  a  church.  Therefore,  600  X  120 
=  72,000  lb.,  the  total  live  load  on  the  girder.  Ans. 


EXAMPLES  FOR  PRACTICE 

1.  What  will  be  the  entire  live  load  on  the  floor  of  a  church 

50  ft.  X  120  ft.?  Ans.  720,000  lb. 

2.  What  live  load  will  a  joist  in  a  city  dwelling  be  required  to  bear, 

the  distance  between  centers  being  14  inches  and  the  span  of  the  joist 
20  feet?  Ans.  1,633  lb. 

3.  A  steel  beam  in  an  office  building  sustains  an  area  of  80  square 
feet.  What  will  be  the  live  load  coming  on  the  beam?  Ans.  5,600  lb. 

4.  A  warehouse  used  for  the  storage  of  South  American  wool  is 
40  feet  wide  and  80  feet  long  inside.  The  girders  extend  across  the 
building  and  divide  it  lengthwise  into  five  bays.  Provided  the  floor 


LOADS  IN  STRUCTURES 


26 


§41 


construction  and  the  girders  weigh  20  pounds  per  square  foot  of 
surface,  what  is  the  total  dead  and  live  load  on  each  girder? 

_  Ans.  104,320  lb. 

11.  In  proportioning  the  live  loads  on  floors,  the  engineer 
cannot  always  exercise  his  own  judgment,  for  if  the  building 
is  to  be  erected  in  a  large  city,  the  live  load  must  comply 
with  the  building  laws.  As  such  laws  are  not  uniform  in  the 
several  cities,  Table  X  is  given  to  show  the  stipulated  live 
loads  in  the  four  largest  cities  in  the  United  States. 


TABLE  X 

ALLOWABLE  LIVE  LOADS  ON  FLOORS  IN  DIFFERENT 

CITIES 


Character  of  Building 

Pounds  per  Square  Foot 

\ 

New  York 

Chicago 

Philadelphia 

Boston 

Buildings  for  public  assembly  . 

90 

IOO 

120 

150 

Buildings  for  ordinary  stores, 

light  manufacturing,  and  light 

storage . 

120 

100 

120 

Dwellings,  apartment  houses, 

tenement  houses,  and  lodging 

houses . 

60 

40 

70 

50 

Office  buildings,  first  floor  .  .  . 

150 

IOO 

IOO 

IOO 

Office  buildings,  above  first  floor 

75 

IOO 

IOO 

IOO 

Public  buildings,  except  schools 

150 

Roofs,  pitch  less  than  20°  .  .  . 

50 

25 

30 

25* 

Roofs,  pitch  more  than  20°  .  . 

30 

25 

30 

25* 

Schools  or  places  of  instruction 

75 

80 

Stables  or  carriage  houses  less 

than  500  square  feet  in  area  . 

75 

40 

Stables  or  carriage  houses  more 

than  500  square  feet  in  area  . 

75 

IOO 

Stores  for  heavy  materials,  ware- 

houses,  and  factories  .... 

150 

150 

250 

Sidewalks . 

300 

Note. — In  Table  X  the  values  given  for  roofs  are  for  snow  and  wind 
loads.  In  the  last  column,  the  roof  loads  marked  with  the  asterisk  (*) 
do  not  include  the  wind  load,  and  the  building  laws  of  Boston  require 
that  a  proper  allowance  for  the  wind  load  exerting  a  pressure  of  30  pounds 
per  square  foot  of  vertical  surface  shall  be  made  in  designing  roofs. 


§41 


LOADS  IN  STRUCTURES 


27 


SNOW  AND  WIND  LOADS 

12.  In  calculating  the  weight  on  roofs,  there  are  two 
other  loads  that  must  always  be  considered  when  obtaining 
the  stresses  on  the  various  members  of  the  truss;  these  are 
snow  and  wind  loads.  When  the  roof  is  comparatively  flat, 
that  is,  when  the  rise  of  the  roof  is  under  12  inches  per  foot 
of  horizontal  distance,  or  is  less  than  \  pitch,  the  snow  load 
is  estimated  at  20  pounds  per  square  foot;  for  roofs  of  more 
than  2  pitch,  or  a  rise  of  more  than  12  inches  per  foot  of  hori¬ 
zontal  distance,  it  is  good  practice  to  assume  the  snow  load 
to  be  12  pounds  per  square  foot.  In  northern  climates,  such 
as  that  of  Canada,  Michigan,  and  New  England,  snow  loads 
50  per  cent,  greater  than  the  preceding  should  be  assumed. 

13.  Wind  Pressure. — The  wind  pressure  depends  on 
the  velocity  with  which  the  air  is  moving.  United  States 
Government  tests  have  determined  that  the  pressure  per 
square  foot  on  a  vertical  surface  is  approximately  represented 
by  the  formula 

P  =  .00492  V\ 

in  which  p  =  pressure,  in  pounds  per  square  foot,  of  vertical 

surface; 

V  —  velocity  of  wind,  in  miles  per  hour. 

This  formula  may  be  expressed  in  the  form  of  a  rule  as 
follows: 

Rule. — The  wind  pressure,  in  pounds  per  square  foot  of 
vertical  surface ,  is  obtained  by  multiplying  the  square  of  the 
velocity  of  the  wind ,  in  miles  per  hour,  by  .00492. 

The  velocity  of  the  wind  varies  from  a  pleasant  breeze  of 
2  or  3  miles  per  hour  to  a  violent  hurricane  or  tornado  of 
100  or  more  miles  per  hour.  Careful  records,  extending 
over  a  period  of  years,  show  that  the  velocity  of  the  wind 
seldom  attains  100  miles  per  hour — probably  not  more  than 
once  in  the  lifetime  of  a  structure.  In  cyclonic  storms,  the 
velocity  of  the  wind  greatly  exceeds  100  miles  per  hour,  and 
structures  cannot  be  built  that  will  withstand  their  fury. 


28 


LOADS  IN  STRUCTURES 


§41 


Table  XI  was  calculated  by  means  of  the  preceding  formula, 
and  it  gives  the  pressure  per  square  foot  for  various  wind 
velocities  up  to  100  miles  per  hour.  Though  the  table  indi¬ 
cates  that  for  100  miles  an  hour  the  pressure  per  square  foot  is 
nearly  50  pounds,  modern  practice  often  allows  only  30  pounds 
per  square  foot  for  large  surfaces,  such  as  the  side  of  a  large 
office  building,  increasing  this  to  45  and  50  for  unloaded 
bridges  and  small  surfaces.  The  reason  for  this  reduction 
is  that  the  average  unit  pressure  on  a  large  surface  is  never 
so  great  as  the  maximum  unit  pressure  on  a  small  surface. 


TABLE  XI 

VELOCITY  AND  FORCE  OF  WIND,  IN  POUNDS  PER 
SQUARE  FOOT,  ON  A  VERTICAL  SURFACE 


Strength  of  Wind 

Miles  per 
Hour 

Feet  per 
Minute 

Feet  per 
Second 

Force  in 
Pounds  per 
Square  Foot 

Hardly  perceptible  .  .  . 

I 

88 

I.47 

.005 

2 

176 

2-93 

.020 

Just  perceptible  .... 

3 

264 

4.4 

•044 

4 

352 

5-87 

.079 

Gentle  breeze . 

5 

440 

7-33 

.123 

io 

880 

14.67 

•492 

Pleasant  breeze  . 

15 

1,320 

22.00 

1. 107 

Brisk  gale . 

20 

1,760 

29-33 

I.968 

25 

2,200 

36.67 

3-075 

High  wind . 

30 

2 , 640 

44.00 

4.428 

35 

3,080 

51-33 

6.027 

40 

3,520 

58.67 

7.872 

Very  high  wind  .... 

45 

3,960 

66.00 

9963 

Storm . 

50 

4,400 

73-33 

1 2 . 300 

6o 

5,280 

88.00 

17.712 

Great  storm . 

70 

6,l6o 

102.67 

24. 108 

8o 

7,040 

H7-33 

31-488 

Hurricane  or  cyclone  .  . 

IOO 

8,800 

146.67 

49.200 

14,  Curved  surfaces,  such  as  would  be  presented  by  cir¬ 
cular  towers  and  stacks,  and  flat  surfaces  not  in  a  vertical 
plane,  as  roofs,  are  subjected  to  less  pressure  than  flat 
vertical  surfaces.  The  pressure  on  a  cylindrical  surface  is 
about  one-half  the  pressure  on  a  flat  surface  having  the  same 


§41 


LOADS  IN  STRUCTURES 


29 


width  as  the  diameter  of  the  cylinder  and  the  same  height. 
If  p\  Fig.  5,  represents  the  direction  and  strength  of  the 
wind  pressure  against  the  roof  a  be,  it  is  the  normal  com¬ 
ponent  p  that  must  be  ascer¬ 
tained  in  order  to  calculate 
the  total  pressure  normal  to 
the  roof,  or  to  determine  the 
stresses  in  the  members  of 
a  roof  frame  or  truss.  The 
other  component  pp  is  act¬ 
ing  upwards  and  in  a  direc¬ 
tion  parallel  with  the  slope. 

The  latter  force  is  not  taken 
into  consideration.  The 
wind,  supposed  to  exert  a  horizontal  pressure  of  40  pounds, 
strikes  the  roof  at  an  angle;  consequently,  the  pressure  p , 
normal  to  the  slope,  is  considerably  less  than  40  pounds, 
unless,  of  course,  the  slope  of  the  roof  is  very  steep.  On 
referring  to  Figs.  5  and  6,  it  will  be  evident  that  the  action 
of  the  horizontal  force  p'  on  the  slope  of  the  roof,  shown  in 
Fig.  5,  is  almost  as  intense  as  on  a  vertical  surface.  How¬ 
ever,  on  the  very  flat  roof,  as  in  Fig.  6,  the  wind  exerts 

hardly  any  force  nor¬ 
mal  to  the  roof  surface, 
because  it  strikes  the 
slope  at  such  an  acute 
angle  that  the  force  pp 
is  nearly  equal  to  p' ,  and  the  tendency  of  the  wind  is  simply 
to  slide  along  the  slope  surface.  The  more  acute  the  angle 
between  the  forces  p'  and  />,  the  greater  is  p,  that  is,  the 
greater  the  pressure  normal  to  the  slope;  whereas,  the  greater 
the  angle  between  these  forces,  the  smaller  will  p  be,  that 
is,  the  less  the  pressure  normal  to  the  slope,  until  they 
approximate  a  right  angle  with  each  other,  when  the 
pressure  p  may  be  disregarded. 

The  full  discussion  of  the  relation  between  p’  and  p  is 
somewhat  more  complex  than  the  one  given  here;  however, 
it  shows  in  a  general  way  why  p  is  more  nearly  equal  to  p ’ 


b 


30 


LOADS  IN  STRUCTURES 


41 


when  a  roof  is  steep  than  when  a  roof  is  flat.  In  the  design 
of  roof  trusses,  a  horizontal  wind  pressure  of  40  pounds  is 
usually  assumed.  • 

TABLE  XII 

NORMAL  WIND  PRESSURE  FROM  HORIZONTAL  PRESSURE 
OF  40  POUNDS  PER  SQUARE  FOOT 


Wind  Pressure 

Horizontal  Rise  per 

Angle  of 

Pitch,  Propor- 

Normal  to 

Foot 

Slope  With 

tion  of  Rise 

Slope 

Inches 

Horizontal 

to  Spall 

Pounds  per 
Square  Foot 

4 . 

l8°  26' 

1 

6 

23.00 

4-8 . 

to 

►— i 

o 

00 

1 

5 

26.1 1 

6 . 

26°  34' 

1 

4 

29.82 

8 . . 

33°4i' 

1 

3 

33-93 

12  . 

45°  o' 

1 

2 

37-71 

16  . 

53°  8' 

2 

3 

39.02 

18  . 

56°  19' 

3 

4 

39-33 

24  . 

63°  26' 

I 

39-75 

15.  Ducliemin’s  Formula. — All  necessary  data  for 
calculating  the  wind  pressure  on  a  roof  with  any  one  of 
the  customary  pitches  and  a  horizontal  wind  pressure  of 
40  pounds  per  square  foot  are  given  in  Table  XII.  The 
formula  by  which  these  pressures  are  determined  is  known 
as  Ducliemin’s  formula.  Its  derivation  is  not  given 
here,  however,  as  it  is  rather  complicated. 

Let  p  —  pressure,  in  pounds  per  square  foot,  normal  to 
slope  of  roof; 

p'  —  wind  pressure,  in  pounds  per  square  foot,  on  a 
vertical  surface; 

x  =  internal  angle  of  roof  with  horizontal  (see  Fig.  4) . 

Then,  according  to  Duchemin, 


P 


2  sin  x 
1  +  sin2  x 


Example. — Find  the  normal  pressure  on  a  roof  of  30°  slope  when 
the  horizontal  wind  pressure  is  40  pounds  per  square  foot. 


841 


LOADS  IN  STRUCTURES 


31 


Solution. — Substituting  values  for  the  letters  in  the  formula, 


.  P 


40  X  2  X  sin  30°  40  X  2  X  .5 

1  -f-  sin*  30°  —  1  +  .25  ~ 


32  lb.  per  sq.  ft.  Ans. 


16.  The  diagram  shown  in  Fig.  7  has  been  made  so  as 
to  facilitate  the  finding  of  the  normal  pressure  p  for  the 
usual  slopes  and  pitches  and  for  horizontal  wind  pressures  of 
20,  30,  and  40  pounds  per  square  foot.  The  values  given  to 
the  three  curves  shown  in  the  diagram  are  found  by  means 
of  the  formula  of  Art.  15. 


Wind  Pressure  Normal  to  Slope  of  Roof  in  Pounds  Per  Square  Foot 


Fig.  7 

The  values  of  the  normal  pressure  for  a  given  slope  and  a 
horizontal  wind  pressure  of  20,  30,  or  40  pounds  may  be 
found  as  follows:  Assume  that  it  is  desired  to  find  the 
normal  pressures  on  a  roof  having  an  angle  with  the  hori¬ 
zontal  of  40°.  Proceed  along  the  horizontal  line  marked  40° 
until  it  intersects  the  curve  marked  20  lb .,  which  represents 
a  horizontal  wind  pressure  of  20  pounds.  The  point  of 
intersection  indicates  the  normal  pressure  p ,  the  value  of 


32 


LOADS  IN  STRUCTURES 


41 


which  is  found  by  drawing  an  imaginary  vertical  line  to  the 
base  line,  which  is  marked  off  in  pounds  of  pressure  per 
square  foot.  It  is  found  that  the  normal  pressure  p  amounts 
to  18.2  pounds  per  square  foot.  Proceeding  in  the  same 
manner,  it  is  found  that  for  horizontal  pressures  of  30  and 
40  pounds,  the  normal  pressures  are  27.3  and  36.4  pounds 
per  square  foot,  respectively. 

17.  In  Fig.  8,  the  normal  force  p  has  been  resolved  into 
its  two  components,  ph  and  pv,  the  former  acting  in  a  hori¬ 
zontal  direction  and 
the  latter  in  a  vertical 
one.  The  force  ph 
tends  to  push  the  roof 
in  a  direction  par¬ 
allel  with  the  wind, 
while  the  force  pv 
tends  to  depress  the 
roof  or,  in  some 
cases,  to  press  it 
sidewise.  In  open 
sheds,  where  the  wind  is  liable  to  strike  the  inner,  far  side  of 
the  shed  roof,  as  shown  in  Fig.  9,  the  effect  of  the  force  pv 
must  be  considered,  as  its  tend¬ 
ency  would  be  to  lift  the  roof. 

Duchemin  has  deduced  the 
following  formulas  for  ph  and  pv\ 

2  sin’  jr 


Fig.  8 


PH=P' 


1  +  sin*  x 


.  ,,2  sin  X  cos  x 

pv  =  p'  - — - 

1  -f  sin  x 


(1) 

(2) 


Example. — A  shed  roof  has  an 
angle  of  slope  with  the  horizontal 
equal  to  18°  26'  and  is  subjected  to  a 
wind  pressure  p'  —  40  pounds  per 
square  foot.  Find  the  values  of  ph  and 
pv  for  the  lee  side  of  the  roof. 

Solution. — Substituting  values  in  formula  1, 


ph  = 


40  X  2  X  sin2  18°  26'  80  X  .1 

1  +  sin2  18°  26'  1  +  .1 


=  7.27  lb.  per  sq.  ft. 


l  +  .l 


§41 


LOADS  IN  STRUCTURES 


33 


Substituting  values  in  formula  2, 


p-v  - 


40  X  2  X  .316  X  .949 

i  +  .1 


21.81  lb.  per  sq.  ft. 


Ans. 


18.  In  order  to  explain  Table  XII  more  fully,  assume  the 
conditions  shown  in  Fig.  10.  The  rise  in  the  slope  ab  is 
6  inches  for  every  12  inches  on  the  horizontal  line  ac\  for 
instance,  at  4  feet  from  a  on  the  horizontal  line  ac,  the  rise 
is  four  times  6  inches,  or  2  feet,  the  angle  included  between 
the  line  of  slope  a  b  and  the  horizontal  base  line  a  c  is  26°  34', 
and  the  pressure  normal  to  the  slope,  according  to  Table  XII, 


is  29.82  pounds  per  square  foot.  Since  the  rise  at  the  center 
is  equal  to  one-half  the  length  of  one-half  the  span,  the  total 
rise  is  one-quarter  of  the  span.  Under  these  conditions,  the 
pitch  of  the  roof,  that  is,  the  ratio  of  the  rise  to  the  span,  is  I, 
and  the  roof  is  said  to  be  }  pitch. 

Example. — (a)  What  will  be  the  dead  load  per  square  foot  of  roof 
surface  on  a  roof  with  a  12-inch  rise  per  foot  horizontal,  the  span  of 
the  iron  trusses  being  50  feet,  and  the  roof  covering  being  made  up  of 
1-inch  white-pine  sheathing,  two  layers  of  Neponset  roofing  felt,  and 
6"  X  18"  shingles  5  inches  to  weather?  (b)  What  will  be  the  wind 
pressure  per  square  foot  normal  to  the  slope?  (c)  If  the  roof  trusses 
are  placed  12  feet  apart,  what  will  be  the  entire  dead  load  on  one 
211  —  36 


34  LOADS  IN  STRUCTURES  §41 

truss?  Fig.  11  shows  a  plan  with  elevation  and  detail  section  of 
the  roof. 

Solution.  —  ( a )  It  is  first  necessary  to  obtain  the  length  of  the  line 
of  slope  ad;  this  is  done  by  calculating  the  hypotenuse  of  the  triangle, 
or  by  laying  the  figure  out  to  scale  and  measuring.  In  the  first  case 
it  is  found  that  ad  measures  about  35.36  ft.  The  area  of  the  roof 
supported  by  one  truss  is  2  X  35.36  X  12  =  848.64  sq.  ft.  According  to 
Table  III,  the  approximate  weight  of  a  roof  truss  of  ^  pitch  and  with 


a  span  of  50  ft.  is  3.182  lb.  per  sq.  ft.  of  roof  surface.  Using  the 
approximate  value  of  3.2  lb.,  the  dead  load  per  square  foot  of  roof 


surface  is,  then,  as  follows: 

Weight  of  supporting  truss .  3.2  lb.  per  sq.  ft. 

Weight  of  white-pine  sheathing,  1  in.  thick  3.0  lb.  per  sq.  ft. 

Weight  of  two  layers  of  Neponset  roofing  felt  .5  lb.  per  sq.  ft. 

Weight  of  shingles .  2.0  lb.  per  sq.  ft. 

Total .  8.7  lb.  per  sq.  ft. 


§41 


LOADS  IN  STRUCTURES 


35 


The  weight  of  the  purlins  supporting  the  sheathing  has  not  been 
estimated,  it  being  safe  in  this  case  to  assume  that  the  weight  used  for 
the  principals,  or  trusses,  is  sufficient  to  cover  this  item.  A  snow  and 
accidental  load  of  12  lb.  per  sq.  ft.  of  roof  surface  should  also  be 
added  to  the  dead  load  to  get  the  entire  vertical  load  on  the  roof. 

(0  The  wind  pressure  normal  to  the  slope  of  this  roof,  according 
to  Table  XII,  for  a  -^--pitch  roof,  is  87.71  lb.,  say  38  lb.  persq.  ft.  Ans. 

(c)  The  area  of  the  roof  supported  by  one  truss  is,  as  previously 
found,  848.64  sq.  ft.  and  the  dead  load  8.7  lb.  per  sq.  ft.  Then, 
848.64  X  8.7  =  7,383.17  lb.  to  be  supported  by  one  truss,  not  including 
the  snow  load.  Ans. 


EXAMPLES  FOR  PRACTICE 

1.  With  the  wind  blowing  at  a  velocity  of  36  miles  per  hour,  what 
is  the  pressure  in  pounds  per  square  foot  of  vertical  surface? 

Ans.  6.38  lb.  per  sq.  ft. 

2.  The  area  of  one  slope  of  a  ^-pitch  roof  is  800  square  feet.  What 
is  the  entire  pressure  on  the  slope  of  the  roof  provided  the  maximum 
horizontal  wind  pressure  is  taken  at  40  pounds  per  square  foot? 

Ans.  30,168  lb. 

3.  In  a  ^-pitch  roof,  the  trusses  are  20  feet  apart  and  the  length 
of  the  roof  slope  is  40  feet.  What  wind  load  is  there  on  each  roof 
truss  if  the  horizontal  pressure  is  40  pounds  per  square  foot? 

Ans.  23,856  lb. 

4.  The  purlins  supporting  a  -f-pitch  roof  are  placed  6  feet  apart, 

and  the  trusses  are  12  feet  from  center  to  center.  What  is  the  load  due 
to  the  wind  on  each  purlin  provided  the  greatest  horizontal  pressure 
is  40  pounds  per  square  foot?  Ans.  2,832  lb.,  nearly 

5.  The  angle  that  the  slope  of  a  roof  makes  with  the  horizontal  is 
40°.  Provided  the  wind  exerts  a  pressure  of  30  pounds  per  square 
foot  of  vertical  surface,  what  is  the  pressure  normal  to  the  slope? 

Ans.  27.3  lb.  per  sq.  ft. 


DISPOSITION  OF  LOADS 

19.  In  warehouses  built  especially  for  the  storage  of 
heavy  merchandise,  where  the  floors  are  likely  at  any  time  to 
be  fully  loaded,  the  beams,  girders,  columns,  and  founda¬ 
tions  are  always  proportioned  for  the  entire  live  and  dead 
loads  on  all  floors.  However,  where  the  building  exceeds 
four  or  five  stories  in  height  and  is  used  for  any  other  pur¬ 
pose  than  for  storage,  as,  for  instance,  a  modern  office  build- 


36 


LOADS  IN  STRUCTURES 


§41 


ing,  it  is  customary  to  assume  that  certain  members,  while 
proportioned  for  the  entire  dead  load,  carry  only  a  certain 
percentage  of  the  live  load. 

In  an  office  building,  or  similar  structure,  it  is  highly 
improbable  that  all  the  floors  or  all  parts  of  the  same  floor 
will  be  fully  loaded  at  the  same  time,  and  in  view  of  this  fact 
it  is  considered  good  practice,  while  proportioning  the  floor- 
beams  for  the  full  live  load,  to  calculate  only  90  per  cent,  of 
the  live  load  on  the  girders  and  columns.  The  term  girders 
as  used  here  indicates  the  larger  beams  that  support  the  floor- 
beams.  It  is  customary  to  proportion  the  columns  supporting 
the  roof  and  the  top  floor  for  the  full  live  load.  The  live  loads 
on  the  columns,  in  each  successive  tier,  from  the  floor  above 
is  reduced  10  per  cent,  until  50  per  cent,  of  the  live  load  is 
reached,  when  such  reduced  loads  are  used  for  all  the  remain¬ 
ing  floors  to  the  basement.  The  economy  obtained  by  this 
disposition  of  the  live  load  is  best  observed  from  Table  XIII, 
which  gives  the  distribution  of  the  assumed  live  loads  on 
the  columns  in  the  several  tiers  of  an  eighteen-story  office 
building. 

The  following  may  serve  to  explain  the  data  given  in 
Table  XIII:  a  represents  the  live  load  on  each  floor,  in 
pounds  per  square  foot;  alf  the  live  load  on  each  floor,  in  pounds 
per  square  foot,  reduced  by  10  per  cent.,  as  ax  =  .90  a;  X a,  the 
sum  of  all  live  loads,  in  pounds  per  square  foot,  on  a  column 
from  all  floors  above,  if  no  reduction  is  made;  and  2  ait  the 
sum  of  all  live  loads,  in  pounds  per  square  foot,  on  a  column 
from  all  floors  above,  if  10  per  cent,  reduction  is  made. 

The  theoretical  percentage  of  saving  resulting  from  the 

reduction  of  10  per  cent,  on  the  upper  floors  is  found  by  the 
v  a  _  v  a 

formula - - - These  percentages  of  saving  are  given 

2  a 

in  the  last  column  of  the  table. 

It  should  be  understood  that  each  column  supports  a  given 
floor  area  and  that  the  load  coming  on  each  column  will 
depend  on  the  extent  of  this  area  multiplied  by  the  live  load, 
in  pounds  per  square  foot  of  floor.  Each  column  carries  not 
alone  this  load,  but  also  the  loads  transmitted  directly  from 


§41 


LOADS  IN  STRUCTURES 


37 


column  to  column.  Thus,  the  column  supporting  the  fifteenth 
floor  supports  also  four  other  columns  above  with  all  their 
loads. 

While  this  system  of  graduating  the  live  loads  on  the 
columns  from  floor  to  floor  is  generally  practiced,  the  amount 

TABLE  XIII 


REDUCTION  OF  DIVE  LOADS  FROM  FLOOR  TO  FLOOR 


Floors 

a 

a,  =  .90  a 

2’a 

2  ci ! 

la  -  Sax 

la 

Roof 

20 

20.00 

20 

20.00 

18 

6o 

60.00 

80 

80.00 . 

1 7 

6o 

54.00 

140 

134.00 

4-3 

16 

6o 

48.60 

200 

182.60 

8.7 

15 

6o 

43.74 

260 

226.34 

12.9 

14 

6o 

39-37 

320 

265.71 

17.0 

13 

6o 

35-43 

380 

301.14 

20.8 

12 

6o 

31.89 

440 

333-03 

24.3 

I  I 

6o 

30.00 

5,00 

363-03 

27.4 

JO 

6o 

30.00 

560 

393-03 

29.8 

9 

6o 

30.00 

620 

423.03 

31.8 

8 

6o 

30.00 

680 

453.03 

33-4 

7 

6o 

30.00 

740 

483-03 

34-7 

6 

6o 

30.00 

800 

513.03 

35-9 

5 

6o 

30.00 

860 

543-03 

36.9 

4 

6o 

30.00 

920 

573-03  ■ 

37-7 

3 

6o 

30.00 

980 

603.03 

38.5 

2 

6o 

30.00 

1 ,040 

633-03 

39-1 

I 

6o 

30.00 

1 ,100 

663.03 

39-7 

of  reduction  at  each  floor  is  a  matter  that  depends  on  the 
judgment  of  the  designer.  The  percentage  of  reduction  is 
often  fixed  by  the  building  laws  of  a  city,  with  which  the 
designer  must  comply.  The  reduction  of  10  per  cent,  at  each 
floor,  the  economy  of  which  is  shown  in  Table  XIII,  is 
conservative,  and  in  most  cases  it  will  be  found  to  be  in 


38  LOADS  IN  STRUCTURES  §41 

accordance  with  the  rules  of  the  building-  departments  of  the 
principal  American  cities. 

20.  In  the  design  of  the  type  of  building  known  as 
skeleton  construction,  that  is,  one  in  which  all  floors  and 
walls  are  supported  on  beams  and  girders  that  transmit 
the  loads  to  columns  and,  in  turn,  are  supported  on  ample 
foundation  footings,  it  is  necessary  to  fix  on  the  general 
arrangement,  disposition,  and  approximate  dimensions  of 
the  component  parts  before  the  dead  load  can  be  computed. 
After  the  calculations  are  made  and  the  structural  details 
are  designed,  the  actual  dead  load  should  be  checked  to  see 
whether  it  approximates  the  assumed  load.  If  any  consider¬ 
able  variation  is  found,  it  can  be  provided  for  by  increasing 
or  diminishing  the  weight  or  thickness  of  the  rolled  steel 
shapes  making  up  the  structural  members,  the  sizes  of  which 
have  already  been  determined. 

Where  permanent  partitions  exist,  they  should  always  be 
figured  in  the  dead  load;  and  where  they  are  directly  above 
a  beam  or  a  girder,  the  member  should  be  proportioned  to 
sustain  the  additional  weight  without  appreciable  deflection. 
Where  movable  partitions  occur  or  where  there  is  a  proba¬ 
bility  of  the  location  of  permanent  partitions  being  changed, 
it  is  customary  to  add  20  pounds  per  square  foot  of  floor 
surface  to  the  dead  load  to  take  care  of  such  contingencies. 

The  foundations  of  an  office  building  should  be  propor¬ 
tioned  for  the  entire  dead  load  and  only  a  portion  of  the  live 
load,  the  latter  being  provided  for  by  making  the  unit  pres¬ 
sure  on  the  footings  and  piers  well  within  the  safe  unit 
bearing  value  of  the  soil.  In  this  way  unequal  settlement 
is  prevented,  as  will  be  explained  in  a  future  Section. 


FIRE  AND  FIRE  INSURANCE 


PURPOSE  OF  FIRE  INSURANCE 

1.  Definition  and  Scope. — Insurance  engineering 

is  the  modern  science  of  reducing  the  chances  of  loss  of 
property  by  fire  to  a  minimum  by  confining  fires  to  the 
smallest  limits  possible.  It  was  first  practiced  on  an  exten¬ 
sive  scale  by  the  factory  mutual  fire-insurance  companies  of 
New  England,  and  has  been  brought  to  a  high  state  of 
development  by  them.  The  proof  of  this  statement  lies  in 
the  fact  that  under  their  system  of  insurance,  the  average 
annual  cost  of  $100  of  insurance  for  a  period  of  6  years  end¬ 
ing  December  31,  1906,  was  .0754  cent. 

Though  first  applied  to  individual  mills  and  factories, 
insurance  engineering  has  been  gradually  extended  to  all 
classes  of  buildings,  even  to  dwellings  and  costly  residences, 
and  the  fire  hazard  of  cities,  taken  as  a  whole,  is  now  dealt 
with  according  to  the  same  principles.  Its  successful  applica¬ 
tion  may  be  said  to  depend  on  a  practical  knowledge  of  a 
number  of  the  more  familiar  branches  of  engineering,  as 
hydraulics,  chemistry,  electricity,  building  construction,  etc. 

2.  Relation  Between  Credit  and  Fire  Insurance. 

A  statement  of  the  close  relation  existing  between  business 
credit  and  fire  insurance  will  give  some  idea  of  the  prominent 
place  occupied  by  insurance  engineering  today.  Thirty  years 
ago  F.  C.  Moore,  ex-president  of  the  Continental  Fire 
Insurance  Company,  of  New  York,  said  regarding  fire  insur¬ 
ance:  “ . it  has  become  a  necessity  of  trade;  without 

its  assuring  protection,  undertakings  of  the  magnitude  at 


COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY.  ENTERED  A'l  STATIONERS'  HALL,  LONDON 


2 


INSURANCE  ENGINEERING 


42 


present  readily  assumed  would  never  be  attempted;  ventures 
are  made,  without  hesitation,  which  would  appal  those 
embarking  in  them  if  liable  to  miscarry  through  a  single 
fire;  large  values  are  boldly  collected  to  meet  the  require¬ 
ments  of  commerce,  where  an  accidental  conflagration  might 
destroy  them  in  a  night;  loans  are  made  by  the  capitalist  on 
insured  buildings  for  many  times  the  value  of  the  land 
on  which  they  stand,  simply  because  the  insurance  policy, 
as  collateral  between  him  and  loss,  makes  it  valuable  for 
security;  merchants  sell  their  goods  on  extended  credits, 
knowing  that,  although  the  misfortune  of  fire  may  Overtake 
the  purchaser,  his  insurance  indemnity  will  enable  him  to 
pay  for  them  not  less  readily  than  before;  vast  industries 
giving  employment  to  thousands  of  operatives  and  support¬ 
ing  whole  towns  by  their  enterprise  testify  not  more  to  the 
energy  of  their  projectors  than  to  the  confidence  they 
repose  in  the  protection  which  insurance  extends  to  their 
undertakings.” 

The  conflagrations  in  Paterson,  Baltimore,  and  San  Fran¬ 
cisco,  in  recent  years,  demonstrated  beyond  a  doubt  the 
utter  dependence  of  merchants  and  manufacturers  on  fire 
insurance  for  means  with  which  to  replace  what  was  destroyed 
by  fire,  and  at  the  same  time  again  emphasized  the  necessity 
of  preventing  conflagrations.  By  conflagration  is  meant  a 
fire  in  which  a  great  number  of  buildings  is  involved. 
Another  significant  feature  of  the  present  situation  is  the 
long  lists  of  firms  and  individuals,  published  at  frequent 
intervals,  who  cannot  obtain  all  the  insurance  they  require 
against  fire.  _ 

CAUSE  AND  PREVENTION  OF  FIRES 


FREQUENCY  OF  FIRES 

3.  The  underlying  cause  of  the  enormous  waste  of 
property  every  year  is  the  frequency  of  fires.  The  total  loss 
for  the  year  1875  was  $78,102,285;  and  for  the  year  1906, 
$518,611,800.  If  fires  occurred  only  occasionally,  there 
would  be  little  need  for  costly  public  fire  departments,  for 


§42 


INSURANCE  ENGINEERING 


3 


the  work  of  insurance  engineers,  or,  indeed,  for  insurance 
against  fire  losses.  But  public  records  show  two  things; 

TABLE  I 

FIRE  RECORD  OF  VARIOUS  CITIES 


Name  of  City 

Population  in 
1900 

Number  of 
Fires  in 
1900 

Number  of 
Fires  in 
1906 

New  York  .... 

3,437,202 

8,405 

12,182 

Chicago . 

1,698,575 

5,503 

.  4,088 

Philadelphia  .  .  . 

1,293,697 

2,944 

3,392 

St.  Louis  .... 

575,238 

2,165 

2,264 

Boston . 

560,892 

1,560 

2,489 

Baltimore  .... 

508,957 

1,438 

1,307 

Cleveland  .... 

381,768 

1,492 

1 ,8ll 

Buffalo . 

352,387 

1 ,020 

1,425 

San  Francisco  .  . 

342,782 

988 

685* 

Cincinnati  .... 

325,902 

1,094 

Pittsburg  .... 

321 ,616 

457 

1 ,200 

New  Orleans  .  .  . 

287,104 

428 

674 

Detroit . 

285,704 

899 

L499 

Milwaukee  .... 

285,315 

i,073 

1,561 

Washington  .  .  . 

278,7 18 

573 

860 

Newark . 

246,070 

620 

745 

Jersey  City  .  •  . 

206,433 

597 

787 

Louisville  .... 

204,731 

385 

1 ,004 

Minneapolis  .  .  • 

202,718 

1 ,002 

875 

Providence  .... 

175,597 

1 ,012 

1,346 

Indianapolis  .  .  . 

169, 164 

1,052 

1,130 

Kansas  City,  Mo.  . 

163,752 

1,127 

L732 

St.  Paul . 

163,065 

82 1 

909 

Rochester  .... 

162,608 

392 

638 

Denver  ..... 

133,859 

545 

*  Only  a  partial  record  for  1906,  the  year  of  the  great  conflagration. 

namely,  that  the  annual  number  of  fires  is  increasing  rapidly, 
and  that  the  number  of  fires  occurring  in  any  given  period  is 


4 


INSURANCE  ENGINEERING 


42 


no  indication  of  the  losses  of  property  caused  by  the  fires. 
Philadelphia  may  be  cited  as  a  case  in  point.  In  1900  there 
were  2,944  fires,  causing-  a  total  property  loss  of  $3,469,063. 
In  1904,  the  total  number  of  fires  was  3,395,  but  the  total 
property  loss  was  only  $1,640,198. 

In  Table  I  is  given  the  fire  record  of  the  twenty-five  largest 
cities  in  the  United  States.  This  record  illustrates  the  fre¬ 
quency  of  fires  and  the  fluctuations  in  the  number  that  occur 
in  the  course  of  a  year. 

In  this  table  the  cities  are  arranged  according  to  popula¬ 
tion.  It  will  be  noticed  that  some  of  the  smaller  cities  have 
more  fires  in  a  year  than  some  of  the  larger  ones. 

Another  phase  of  the  frequency  of  fires  is  the  number  that 
occur  in  large  manufacturing  establishments,  the  destruction 
of  which  would  very  often  mean  a  much  heavier  property  loss 
than  would  result  from  the  burning  of  the  same  number  of 
buildings  of  cheaper  construction,  or  occupied  for  different 
purposes.  During  1906,  ninety-five  fires  occurred  in  a  large 
machine-shop  plant  in  Philadelphia. 

Fire-marshal  laws,  which  provide  for  the  investigation  of 
fires,  have  had  a  wholesome  effect,  but  they  have  not  solved 
the  problem  of  the  annual  fire  waste. 


CAUSES  OF  FIRE 

4.  A  distinction  must  be  made  between  the  causes  of  fire 
and  the  causes  of  losses  resulting  from  fires.  Losses  of 
property  by  fire  depend,  of  course,  on  the  occurrence  of  fire, 
but  the  extent  of  a  loss  is  influenced  greatly  by  other  factors, 
or  conditions,  that  favor  the  spread  of  a  fire  when  once  fairly 
started. 

Generally  speaking,  carelessness  and  apathy  are  the  most 
common  causes  of  fire.  “No  one  can  carefully  read  the 
figures  contained  in  the  Fire  Marshal’s  report  to  me,”  said 
Fire  Commissioner  Francis  J.  Lantry,  of  New  York  City, 
commenting  on  the  report  for  1906,  “without  being  astounded 
at  the  number  of  fires  that  could  have  been  prevented  by  the 
exercise  of  very  ordinary  caution.  I  think  that  if  the  public 


42 


INSURANCE  ENGINEERING 


5 


mind  is  sufficiently  aroused  for  the  proper  exercise  of  this 
caution,  the  people  generally  can  become  of  great  service  to 
this  department  in  the  prevention  of  fires.  The  Fire  Mar¬ 
shal’s  Bureau  is  for  the  investigation  and  determination  of 
the  causes  of  fires,  and  the  head  of  that  bureau  reports  that 
in  the  Boroughs  of  Manhattan,  the  Bronx,  and  Richmond, 
among  the  principal  causes  of  fires  ascertained  by  his  investi¬ 
gation,  887  were  due  to  carelessness  with  matches  and  228 
due  to  children  playing  with  matches  or  fires.  Carelessness 
.  in  the  use  of  lighted  cigars  and  cigarettes  caused  401  fires; 
overheated  stoves,  stovepipes,  etc.  are  charged  with  the 
responsibility  for  419  fires;  bonfires,  brush  fires,  etc.  are 
charged  with  282;  carelessness  with  candles,  tapers,  etc.,  386; 
gaslight  in  contact  with  curtains,  etc.,  216;  lamps,  kerosene, 
etc.  upsetting  or  exploding,  161.” 

5.  Underwriters  divide  the  causes  of  fire  into  two  heads: 
common  ca?ises  (common  hazards)  and  special  causes  (special 
hazards) . 

•  . 

The  common  causes  are  artificial  lighting  (arc  electric, 
incandescent  electric,  ordinary  city  gas,  gasolene  gas,  acety¬ 
lene  gas,  kerosene-oil  lamps,  kerosene-oil  lanterns,  kerosene- 
oil  torches,  and  candles);  heating  (steam,  hot  air,  coal  stove, 
gasolene  stove,  and  oil  stove);  power  (shafting  and  bear¬ 
ings,  steam  engines,  gas  engines,  gasolene  engines,  and 
electric  motors);  boiler,  or  fuel  (coal  fuel,  waste  material  or 
refuse  used  as  fuel,  overheated  woodwork,  sparks  from  stack, 
defective  chimney,  and  ashes);  rubbish,  or  sweepings;  oily 
material  (oily  waste  and  other  oily  material);  smoking; 
lightning;  sparks  from  locomotives;  and  miscellaneous. 

The  special  causes  are  those  arising  from  manufacturing 
processes,  as  in  cotton  mills,  woolen  mills,  rubber  factories, 
iron  and  steel  mills,  shoe  factories,  breweries,  etc.,  and  may 
be  divided  in  general  as  follows:  Storage  and  handling  of 
raw  stock;  preparing  raw  stock;  making,  or  general  processes 
of  manufacture;  finishing;  and  disposal  of  waste  material. 

Common  causes  and  special  causes  of  fire  are  found  in  all 
kinds  of  manufacturing  establishments,  but  they  vary  greatly. 


6 


INSURANCE  ENGINEERING 


§42 


Special  fire  hazards  consist  chiefly  in  the  nature  of  the  raw 
material  worked,  the  presence  of  large  quantities  of  raw 
material  and  finished  goods  (when  of  a  highly  combustible 
nature),  and  the  disposal  of  the  refuse  resulting  from  the 
processes  of  manufacture. 


PREVENTION  OF  FIRES 

6.  The  terrible  consequences  of  fire,  as  evidenced  by  the 
record  of  the  past  35  years  or  more,  is  the  strongest  argu¬ 
ment  that  can  be  advanced  for  preventing  fires.  Aside 
from  the  enormous  losses  of  property,  thousands  of  persons 
have  lost  their  lives  in  recent  years  in  such  fires  as  the 
Windsor  Hotel  fire  in  New  York  City,  on  March  17,  1899; 
the  Iroquois  Theater  fire  in  Chicago,  on  December  30,  1903; 
the  excursion  steamboat  General  Slocum  fire,  in  the  East 
River,  New  York  City,  on  June  15,  1904;  also,  the  many 
fires  in  tenements,  apartments,  hotels,  public  halls,  boarding 
houses,  college  dormitories,  and  even  private  dwellings 
might  be  cited.  Another  recurring  feature  of  the  annual  fire 
waste  is  the  long  list  of  conflagrations  in  small  places,  as, 
for  example,  the  fire  in  Bisbee,  Arizona,  on  June  29,  1907, 
which  destroyed  more  than  200  houses;  the  fire  in  Coal 
Creek,  Colorado,  on  the  same  date,  which  destroyed  more 
than  100  buildings;  the  fire  in  North  Lawrence,  New  York, 
on  July  5,  1907,  which  destroyed  38  business  buildings  and 
dwellings — practically  the  entire  place. 

7.  Fires  may  be  prevented  by  observing  the  lessons 
taught  by  fires  and  anticipating  more  fires  from  well-known 
or  similar  causes.  In  large  mercantile  buildings,  factories, 
and  warehouses,  probably  the  greatest  precaution  is  cleanli¬ 
ness.  Accumulations  of  dirt  and  refuse  are  a  constant 
source  of  fire  and  favor  the  spreading  of  fire.  This  applies 
particularly  to  accumulations  of  oily  refuse,  such  as  cotton 
waste  that  has  been  used  for  wiping  machinery,  oily  iron 
turnings,  polishing  rags,  etc.,  and  accumulations  of  refuse 
of  a  highly  combustible  nature,  as  dust,  shavings,  sawdust, 
packing  materials,  etc.  Such  refuse  should  never  be  per- 


i 


42 


INSURANCE  ENGINEERING 


7 


mitted  to  remain  in  a  building  overnight,  or  over  a  holiday. 
When  such  refuse  is  produced  in  large  quantities,  it  should 
be  removed  by  an  exhaust  blower  system,  with  a  dust  sepa¬ 
rator  and  a  vault  for  the  heavier  refuse.  Oily  waste  should 
be  collected  in  approved  metal  receptacles,  such  as  are 
recommended  by  underwriters,  and  these  should  be  emptied 
frequently.  The  amount  of  refuse  made  in  a  day  will 
suggest  the  danger  from  fire. 

8.  All  woodwork  should  be  kept  free  from  accumulations 
of  oily  drippings  and  from  proximity  to  boilers,  furnaces, 
chimneys,  stacks,  steam  pipes,  portable  heaters  and  furnaces, 
gas  jets,  etc.  Inflammable  and  volatile  oils  should  not  be 
used  near  open  lights  or  fires,  and  lanterns  and  open  lights 
should  not  be  carried  into  rooms  where  the  atmosphere  is 
charged  with  such  vapors.  Smoking  and  the  carrying  of 
matches  (other  than  safety  matches)  should  be  prohibited. 
Gasolene-gas,  acetylene-gas,  and  electric  lighting  should  be 
used  only  in  accordance  with  the  latest  recommendations  of 
the  underwriters.  Hot  ashes  should  not  be  collected  in 
wooden  receptacles,  nor  should  they  be  thrown  on  wooden 
floors  or  piled  against  wooden  walls  or  partitions.  Large 
quantities  of  inflammable  or  volatile  oils  should  not  be  stored 
in  the  main  building.  Separate  small  buildings  are  pre¬ 
ferred  for  the  storage  of  the  bulk  of  these  oils,  and  fireproof 
rooms  should  be  constructed  to  store  during  the  night  the 
small  quantities  left  over  from  the  day’s  work. 

In  most  manufacturing  processes  there  are  dangers  from 
fire  peculiar  to  each.  These  the  manufacturers  and  mill 
superintendents  must  understand  and  appreciate.  The  care, 
order,  and  management  of  a  large  establishment  are  an  index 
to  the  danger  from  fire. _ 

SPREADING  OF  FIRES 

9.  The  cause  of  the  conflagrations  that  have  devastated 
cities  and  towns  and  wiped  out  settlements  has  been  the  ease 
with  which  the  original  fire  spread  to  all  parts  of  the  first 
building,  passed  beyond  those  limits  by  working  into  adjoin¬ 
ing  buildings  and  by  jumping  streets,  and  thence  to  block 


8 


INSURANCE  ENGINEERING 


§42 


after  block  of  buildings,  in  every  direction,  until  the  fire  Was 
checked  in  some  manner  or  burned  itself  out.  Sparks  and  • 
brands  are  carried  long  distances  by  the  wind,  and  often 
start  fresh  fires.  The  hot  gases  of  a  conflagration  will 
ignite  buildings  located  blocks  away  from  the  seat  of  the 
fire.  An  earthquake  will  start  a  number  of  fires  simul¬ 
taneously.  The  occurrence  of  a  number  of  fires  at  the  same 
time,  or  close  after  one  another,  produces  the  most  demor¬ 
alizing  effect  imaginable  on  a  public  fire  department.  Not 
only  the  firemen,  but  all  the  safeguards  provided  for  such  an 
emergency,  are  taxed  to  the  utmost,  perhaps  to  the  point  of 
breaking  down.  Apparatus  and  hose  are  destroyed,  and 
large  quantities  of  water  are  wasted  through  the  breaking  of 
pipes,  thus  reducing  the  pressure  and  the  supply.  It  is  not 
uncommon  for  cities  to  ask  for  help  from  other  cities  at  such 
times,  but  the  value  of  the  assistance  of  other  cities  depends 
on  whether  the  same,  or  nearly  the  same,  standard  of  hose 
and  hydrant  couplings  is  used. 

10.  Causes  of  tlie  Spreading:  of  Fires. — Following 
are  some  of  the  prominent  causes  of  the  spreading  of  fires 
from  the  place  of  origin:  Excessive  height  of  buildings;  com¬ 
bustible  or  weak  walls;  combustible  or  weak  roofs;  lack  of 
parapet  walls;  the  presence  of  wooden  cornices;  superstruc¬ 
tures;  awnings,  signs,  etc.;  wooden  bridges  connecting  build¬ 
ings;  combustible  or  weak  division  walls;  concealed  spaces 
in  division  walls;  inflammable  interior  surfaces  (varnished, 
oiled,  or  painted  wood,  papier  mache,  etc.);  combustible  or 
weak  partitions;  concealed  spaces  in  partitions;  combustible 
or  weak  floors;  concealed  spaces  between  floors  and  ceil¬ 
ings;  combustible  floor  supports;  unprotected  metallic  floor 
supports;  combustible  ceilings;  concealed  spaces  in  roofs; 
unprotected  windows,  doorways,  and  skylights;  open  stair¬ 
ways,  elevator  shafts,  hoistways,  and  dumbwaiter  shafts; 
chutes  without  doors  at  openings;  and  belt  and  shaft  open¬ 
ings  in  walls  and  floors. 

Smoke  explosions  are  undoubtedly  a  factor  in  the  spread¬ 
ing  of  fire.  They  force  out  windows  and  thereby  increase 


42 


INSURANCE  ENGINEERING 


9 


the  draft;  but  this  danger  appears  to  be  confined  to  build¬ 
ings  several  stories  in  height  and  of  rather  large  floor  areas. 

11.  Causes  of  Conflagrations. — Conflagrations  are 
generally  due  to  the  poor  construction  of  buildings;  unpro¬ 
tected,  exposed  window  openings;  unprotected  communi¬ 
cations  between  buildings;  narrow  streets;  lack  of  proper 
building  laws;  non-enforcement  of  building  laws;  lack  of 
fire  limits;  lack  of  proper  water  supply;  lack  of  sufficient 
hydrants;  lack  of  modern  fire  departments;  lack  of  ordi¬ 
nance  restricting  the  handling  and  storage  of  combus¬ 
tibles  and  explosives;  lack  of  ordinance  compelling  the 
proper  disposal  of  refuse;  lack  of  ordinance  compelling  safe 
electrical  installations  inside  of  buildings;  and  lack  of 
ordinance  compelling  the  placing  of  all  outside  wires  under¬ 
ground. 

Too  much  stress  cannot  be  laid  on  the  importance  of 
window  protection,  even  on  street  fronts.  In  the  Baltimore 
and  San  Francisco  conflagrations,  modern  so-called  fireproof 
office  buildings  (skeleton  steel-frame  construction)  were 
badly  damaged  by  fire  because  the  windows  were  not  pro¬ 
tected  against  the  ingress  of  fires  starting  outside  of  the 
buildings — “exposure”  fires.  A  building  that  cannot  be 
damaged  by  fire  makes  a  good  barrier  to  the  spreading  of 
fire.  The  so-called  fireproof  buildings  in  Baltimore  and  San 
Francisco  only  partly  served  that  purpose. 

12.  Conflagration  Breeders. — The  record  of  the  past 
shows  that  conflagrations  can  start  in  almost  any  kind  of 
property,  but  there  are  classes  of  buildings  that  underwriters 
call  conflagration  breeders,  because  fires  that  get  a  good 
start  in  them  are  almost  sure  to  develop  into  conflagrations. 
Department  stores  are  of  this  class — buildings  of  large  floor 
areas,  filled  with  combustible  material;  especially  the  type 
of  department  store  with  a  large  light  well  extending  from 
the  first  floor  to  the  roof,  making  the  entire  building  prac¬ 
tically  one  undivided  area  and  “subject  to  one  fire.” 


10 


INSURANCE  ENGINEERING 


§42 


FIREPROOF  CONSTRUCTION 

13.  The  development  of  the  United  States  has  been 
phenomenal.  A  point  has  been  reached  where  cities  are 
built  to  order,  as  in  the  case  of  Gary,  Indiana,  the  new  city 
that  has  been  built  by  the  United  States  Steel  Corporation. 
But  in  spite  of  the  great  progress  in  this  direction,  little 
thought  has  been  given  to  the  subject  of  permanency — it 
has  been  well  said  that  “we  build  to  burn.”  There  is  no 
business  economy  in  such  a  method. 

Building  operations  in  Greater  New  York  amounted,  in 
1906,  to  $228,551,971;  in  Chicago,  during  the  same  period, 
$64,822,030;  in  Philadelphia,  $36,957,520;  in  St.  Louis, 
$29,938,693;  in  Boston,  $23,064,741;  and  in  San  Francisco, 
$33,779,192.  These  amounts  include  the  cost  of  alter¬ 
ations  and  repairs,  which  in  Greater  New  York  in  1906 
reached  the  sum  of  $25,000,000. 

A  very  small  percentage  of  the  buildings  in  the  United 
States  pretend  to  be  fireproof.  Wooden  construction  pre¬ 
dominates,  and  a  large  majority  of  the  brick  buildings  are  of 
a  type  that  is  as  easily  destroyed  by  fire  as  are  wooden  build¬ 
ings,  because  of  their  combustible  interiors — thin  wooden 
floors  supported  on  joists  of  small  dimensions,  etc.,  and  roofs 
of  the  same  construction. 

Nowadays,  wood  can  easily  be  dispensed  with  in  the  con¬ 
struction  of  all  classes  of  buildings.  It  is  no  longer  required 
even  for  trim.  A  fireproof  dwelling  costs  very  little  more 
than  one  of  wood.  For  buildings  located  where  there  is  no 
public  fire  department,  fireproof,  construction  is  imperative. 

14.  Types  of  Fireproof  Construction. — There  are 
three  types  of  building  construction  that  resist  fire  success¬ 
fully,  namely,  slow-burning ,  or  mill ,  construction;  fireproofed, 
skeleton  steel-frame  construction;  and  reinforced-concrete  con¬ 
struction. 

15.  Slow-burning,  or  mill,  construction  has  been 

employed  extensively  for  mills,  factories,  and  storehouses 
up  to  five  stories  in  height,  and  consists  chiefly  of  substantial 


l 


§42 


INSURANCE  ENGINEERING 


11 


brick  walls;  heavy  wooden  floors  without  openings,  sup¬ 
ported  on  heavy  wooden  beams  and  posts;  and  roofs  of 
similar  construction.  The  frame  of  the  building  may  be 
supported  by  the  walls,  or  it  may  be  self-sustaining.  Stairs, 
elevators,  and  power  transmission  are  placed  in  brick  towers, 
all  openings  to  the  main  building  being  protected  by  approved 
fire-doors.  The  late  Edward  Atkinson  described  mill  con¬ 
struction  as  follows: 

“1.  Mill  construction  consists  in  so  disposing  the  timber  and 
plank  in  heavy  solid  masses  as  to  expose  the  least  number 
of  corners  or  ignitible  projections  to  fire,  to  the  end  also 
that  when  fire  occurs  it  may  be  more  readily  reached  by 
water  from  sprinklers  or  hose. 

“2.  It  consists  in  separating  every  floor  from  every  other 
floor  by  incombustible  stops — by  automatic  hatchways,  by 
encasing  stairways  either  in  brick  or  other  incombustible 
partitions — so  that  a  fire  shall  be  retarded  in  passing  from 
floor  to  floor  to  the  utmost  that  is  consistent  with  the  use  of 
wood  or  any  material  in  construction  that  is  not  absolutely 
fireproof.” 

President  Atkinson  cautioned  architects  and  builders  against 
the  misuse  and  abuse  of  “mill”  construction  in  the  following 
language: 

“1.  Mill  construction  does  not  consist  in  disposing  a 
given  quantity  of  materials  so  that  the  whole  interior  of  a 
building  becomes  a  series  of  wooden  cells,  being  pervaded 
with  concealed  spaces,  either  directly  connected  each  with 
the  other  or  by  cracks  through  which  fire  may  freely  pass 
where  it  cannot  be  reached  by  water. 

“2.  It  does  not  consist  in  an  open-timber  construction  of 
floors  and  roof  resembling  mill  construction,  but  of  light  and 
insufficient  size  in  timbers  and  thin  planks,  without  fire-stops 
or  fire-guards  from  floor  to  floor. 

“3.  It  dees  not  consist  in  connecting  floor  with  floor  by 
combustible  wooden  stairways  encased  in  wood  less  than 
2  inches  thick. 

“4.  It  does  not  consist  in  putting  in  very  numerous  divi¬ 
sions  or  partitions  of  light  wood. 

211—37 


12 


INSURANCE  ENGINEERING 


42 


“5.  It  does  not  consist  in  sheathing  brick  walls  with 
wood,  especially  when  the  wood  is  set  off  from  the  wall  by 
furring,  even  if  there  are  stops  behind  the  furring. 

“6.  It  does  not  consist  in  permitting  the  use  of  varnish 
on  woodwork  over  which  fire  will  pass  rapidly. 

“7.  It  does  not  consist  in  leaving  windows  exposed  to 
adjacent  buildings  unguarded  by  fire-shutters  or  wired  glass.” 

16.  Mill  construction  has  been  abused  by  architects  by 
adopting  only  a  few  of  its  good  features  and  by  disregarding 
its  limitations.  On  the  night  of  February  11,  1905,  the  new 
building  of  the  Schwabacher  Hardware  Company,  at  the 
southwest  corner  of  First  Avenue  (South)  and  Jackson 
Street,  Seattle,  Washington,  was  practically  destroyed  by 
fire.  It  was  eight  stories  in  height,  and  70  ft.  X  120  ft.,  with 
brick  walls,  two  of  them  being  blank.  The  size  of  floor 
posts,  the  use  of  combustible  material  as  waterproofing 
between  the  flooring,  and  the  fact  that  the  building  was 
17  feet  higher  than  permitted  by  law  had  been  criticized  by 
the  building  department,  but  it  was  said  at  the  time  that 
these  objections  were  finally  waived.  There  were  no  auto¬ 
matic  sprinklers.  The  fire  started  in  a  box  of  waste  or 
rubbish  on  the  second  floor  and  spread  to  a  light  wooden 
partition.  In  less  than  an  hour  the  building  collapsed. 
“The  giving  way  of  the  roof,  which  is  said  to  have  been 
able  to  bear  only  half  the  prescribed  live  weight  per  square 
foot,  presumably  pulled  out  some  of  the  strap-iron  joist 
hangers,  which  at  the  suspension  points  entered  the  walls 
4  inches.  There  were  no  ledges.  A  large  section  of  the 
south  wall  fell  out  and  at  intervals  other  walls  fell  outward 
until  everything  down  to  the  first  floor  was  wrecked.”  The 
fire  department  lost  nearly  all  its  long  ladders  and  500  feet 
of  hose. 

17.  Fireproofed  skeleton  steel-frame  construction 
consists,  as  the  name  implies,  of  a  skeleton  frame  of  struc¬ 
tural  steel  that  is  completely  encased  in  fireproofing  so  as 
to  protect  it  from  the  effects  of  fire.  Terra  cotta  burned 
at  a  temperature  of  from  2,000°  to  2,500°  F.  is  the  fire- 


§42 


INSURANCE  ENGINEERING 


13 


proofing-  commonly  used.  It  is  made  in  shapes  to  fit  the 
various  members  of  the  steel  frame,  and  it  is  used  for  floor 
and  roof  arches  and  for  partitions.  It  is  light  and  strong — 
columns  of  terra-cotta  blocks  have  been  used  in  the  place  of 
steel  columns  for  carrying  heavy  loads.  Brick  and  concrete 
are  also  used  for  fireproofing  and  for  floors  and  partitions. 
The  concrete  is  usually  reinforced,  either  with  steel  rods  or 
with  expanded  me, tal.  The  front  walls  of  steel-frame  build¬ 
ings  are  usually  of  stone  and  brick,  and  the  other  curtain 
walls  are  built  of  brick  or  terra-cotta  blocks.  Without  com¬ 
plete  fireproofing,  no  steel-frame  building  could  withstand 
the  heat  coming  from  an  intense  fire,  and  its  use  for  very 
high  buildings,  or  even  buildings  more  than  two  stories  in 
height,  would  probably  be  prohibited  by  law. 

18.  Reinforced-concrete  construction  produces 
monoliths — buildings  in  which  the  foundations,  walls,  floors, 
floor  supports,  partitions,  roofs  and  roof  supports,  stairs,  etc. 
are  all  constructed  of  concrete  reinforced  with  steel.  Terra 
cotta  and  reinforced  concrete  are  considered  an  ideal  com¬ 
bination  for  fireproof  construction. 

% 

19.  Object  and  Requirements  of  Fireproof  Con¬ 
struction. — The  object  of  fireproof  construction  should  be 
to  confine  a  fire  to  certain  prescribed  limits.  To  do  this,  all 
communications  between  adjoining  rooms  and  buildings,  and 
between  floors,  must  be  protected  to  prevent  the  spreading 
of  fire;  and  all  exposed  windows  should  be  protected  against 
“exposure”  fires.  Wooden  window  frames  and  sashes 
should  not  be  used. 

In  New  York  City,  fireproofing  systems  for  floors  must  pass  a 
test  of  4  hours’  exposure  to  a  temperature  averaging  1,700°  F., 
after  which  the  upper  side  is  flooded  and  water  is  thrown  on 
the  under  side.  After  this  a  load  is  put  upon  the  floor.  The 
deflections  caused  by  the  temperature  are  noted  with  survey¬ 
or’s  instruments. 

v 

Comprehensive  building  laws,  properly  enforced,  are  the 
chief  safeguards  against  poor  construction. 


14 


INSURANCE  ENGINEERING 


§42 


EXTINGUISHMENT  OF  FIRES 

20.  Ample  facilities  for  extinguishing  fire  and  good 
building  construction  go  hand  in  hand.  While  the  former 
are  doing  their  work,  the  latter  helps  materially  by  resisting 
the  spreading  of  the  fire.  It  is  a  combination  of  these  two 
features  that  makes  small  losses  from  fire  possible.  The  low 
cost  of  insurance  under  the  factory  mutual  system  depends 
on  this  combination  and  its  constant  maintenance. 

Fire-extinguishing  facilities  divide  themselves  into  two 
heads,  namely,  private  and  public. 

21.  Private  fire  protection  may  consist  of  casks  and 
pails  of  water,  pails  of  sand,  pails  containing  a  chemical 
solution;  bucket  tanks  containing  a  chemical  solution  and  a 
nest  of  pails  immersed  in  the  solution;  liquid  chemical  extin¬ 
guishers;  inside  standpipes  extending  from  the  basement  to 
the  roof,  with  hose  connections  and  hose  for  each  floor  and 
with  a  deluge  nozzle  on  the  roof;  outside  standpipes  or 
connections,  with  hose;  an  equipment  of  automatic  sprinklers; 
outside  hydrants  with  hose  houses  built  over  them;  a  watch¬ 
man  (perhaps  several  in  very  large  plants)  who  makes  rounds 
at  regular  intervals  at  night,  on  Sundays,  and  holidays  and 
records  his  rounds  on  a  special  clock  for  the  purpose;  ther- 
mostats;  an  auxiliary  fire-alarm  system  connected  with  the 
public  fire-alarm  system;  a  central-station  service  for  super¬ 
vising  the  watchman  and  automatic  sprinkler  equipments  (in 
large  cities);  fire-escapes,  ladders,  platforms,  etc. 

22.  Automatic  sprinklers  are  small  water  valves 
held  shut  by  fusible  solder  that  will  melt  at  about  165°  F. 
They  are  placed  on  the  ceilings  of  rooms,  and  are  sup¬ 
plied  with  water  from  two  or  more  sources  through  a 
system  of  piping.  The  water  supplies  usually  consist  of  a 
tank  having  a  capacity  of  5,000  gallons  or  more,  located  on  a 
trestle  above  the  roof  of  a  building  (or  on  a  tower  built  up 
from  the  ground),  with  the  bottom  at  a  height  that  will  give 
a  sufficient  water  pressure  on  the  highest  lines  of  sprinklers; 
a  fire-pump  with  a  capacity  of  500  gallons  or  more  per  minute; 


§42 


INSURANCE  ENGINEERING 


15 


a  connection  with  the  public  water  system;  etc.  The  sprinklers 
are  so  distributed  as  to  have  one  for  every  100  square  feet 
(10  ft.  XlO  ft.)  of  floor  area  or  less,  a  room  50  ft.  X  100  ft. 
requiring  about  fifty  sprinklers.  They  are  operated  by  the 
heat  from  a  fire,  the  fusible  link  melting  and  falling  away, 
thereby  opening  the  sprinkler  and  allowing  the  water  to  be 
freely  distributed  on  the  ceiling  and  floor  immediately  above 
and  below  it.  For  a  period  of  10  years  (1897-1907),  75  per 
cent,  of  fires  in  buildings  protected  by  automatic  sprinklers 
were  extinguished  by  the  operation  of  an  average  of  ten 
sprinklers.  It  is  important  that  all  parts  of  a  building  be 
under  the  protection  of  automatic  sprinklers,  that  the  water 
supplies  be  ample,  and  that  all  valves  controlling  the  flow  of 
water  in  the  pipes  be  kept  open.  The  exceptions  to  these 
general  rules  are  clearly  stated  in  the  standards  of  the  under¬ 
writers.  The  invention  of  automatic  sprinklers  revolu¬ 
tionized  the  protection  of  individual  buildings  against  fire, 
and  their  use  has  resulted  in  a  great  saving  to  capital. 

23.  Public  fire  protection  consists  of  a  waterworks 
system  supplying  fire-hydrants  distributed  throughout  the 
streets  of  a  city  or  town,  a  fire-alarm  telegraph  system  for 
giving  alarms  of  fire,  and  a  fire  department  equipped  with 
steam  fire-engines,  hose  wagons,  hook-and-ladder  trucks, 
water  towers,  fire-boats,  etc.  In  various  cities,  salvage  corps 
are  maintained.  These  corps  render  very  valuable  service 
by  putting  out  small  fires  before  they  can  spread  and  by 
covering  up  perishable  goods  with  tarpaulins,  by  doing 
watch  service,  etc. 

The  greatest  need  of  cities,  in  view  of  the  grave  likelihood 
of  general  conflagrations  among  the  buildings  in  the  business 
sections  (the  congested  districts),  is  an  ample  supply  of 
water  distributed  through  large  street  mains  at  a  high  pres¬ 
sure,  so  as  to  prevent  fires  from  becoming  conflagrations. 
The  intense  heat  of  spreading  fires  turns  the  ordinary  hose 
stream  into  steam.  Volumes  of  water  under  a  heavy  pres¬ 
sure  is  the  only  sure  means  of  extinguishing  threatening 
fires.  Such  systems  are  called  high-pressure  fire-main  systems. 


16 


INSURANCE  ENGINEERING 


42 


Philadelphia  has  one,  and  a  similar  system  is  installed  in  the 
Borough  of  Manhattan,  Greater  New  York.  River  water  is 
utilized.  Other  cities  have  special  fire-main  systems  that 
are  fed  by  fire-boats. 

For  small  cities  or  towns,  deluge  nozzles  mounted  on 
battery  wagons  and  supplied  by  a  number  of  hose  streams 
are  invaluable  in  concentrating  a  large  volume  of  water  on  a 
serious  fire. 

24.  Many  large  factories  are  protected  throughout  with 
automatic  sprinklers,  standpipes  and  hose,  casks  and  pails  of 
water,  liquid  chemical  extinguishers,  outside  fire-hydrants, 
watchman  service,  etc.  The  employes  are  formed  into 
private  fire  companies  and  are  drilled  in  the  use  of  the 
private  fire  appliances.  Such  private  fire  protection  has 
given  rise  to  the  designation  among  insurance  men  of 
“improved  risk.”  The  term  risk  as  used  here  means  the 
degree  of  exposure  to  fire,  improved  risk  indicating  that  the 
chances  of  loss  by  fire  are  lessened.  These  risks  merit 
the  lowest  rates  of  insurance. 


COST  OF  INSURANCE 


ADJUSTMENT  OF  RATES 

25.  Insurance  rates,  or  premiums,  are  the  prices 
charged  for  insurance  against  loss  by 'fire.  A  rate  of 
60  cents  means  60  cents  per  $100,  or  that  $1,000  of  insurance 
for  one  year  will  cost  $6.  For  a  long  time  no  intelligent 
attempt  was  made  to  ascertain  the  cost  of  the  different  ele¬ 
ments  of  fire  hazards;  that  is,  the  difference  between  the 
cost  of  insuring  a  wooden  building  and  a  brick  building; 
the  difference  between  the  cost  of  insuring  a  building  with 
an  elevator  in  an  open  shaft  and  a  building  with  an  elevator 
in.  a  closed  shaft;  the  difference  between  the  cost  of  insur¬ 
ing  a  building  in  a  city  under  the  protection  of  a  public-paid 
fire  department  and  a  building  in  a  locality  not  under  such 
public  protection;  etc. 


§42 


INSURANCE  ENGINEERING 


17 


By  carefully  studying-  the  causes  of  fire  and  fire  losses, 
underwriters  have  been  able  to  determine  approximately  the 
cost  of  defects  in  the  construction  of  buildings  that  favor 
heavy  losses  from  fire,  the  cost  of  “exposure”  from  adjoin¬ 
ing  buildings  or  buildings  within  a  certain  distance  (due  to 
lack  of  window  protection,  lack  of  fire-walls  between  adjoin¬ 
ing  buildings,  continuous  wooden-boxed  cornices  on  a  row 
of  buildings,  etc.),  the  cost  of  management  of  premises  that 
is  conducive  to  fires  due  to  neglect,  the  cost  of  insufficient 
or  unreliable  facilities  for  fighting  fires,  etc.  These  numer¬ 
ous  items  have  been  scheduled  for  the  information  of 
owners  of  property,  merchants,  and  manufacturers,  to  give 
them  an  idea  of  how  the  cost  of  insurance  is  arrived  at  and 
how  it  may  be  reduced. 

26.  All  buildings  are  compared  with  a  standard,  and  in 
making  insurance  rates  credits  are  given  for  the  following 
desirable  features:  Small  areas,  fire-resistive  floors,  water¬ 
proof  floors,  floors  arranged  for  flooding,  fireproof  floors 
(especially  in  the  first  story),  incombustible  ceilings  and 
partitions,  parapet  walls  between  adjoining  buildings  (all 
openings  in  division  and  party  walls  must  be  protected  in  an 
approved  manner  to  make  them  “fire-walls”)  fireproof 
enclosures  for  elevators  and  stairs,  fire-resistive  coverings 
for  all  other  openings  in  floors  and  walls,  approved  protec¬ 
tion  for  window  openings  in  walls  facing  other  buildings, 
etc.  Credits  are  also  given  for  the  introduction  of  private 
fire  protection,  such  as  standpipe  and  hose  equipments, 
casks  and  pails  of  water,  chemical  pails,  liquid  chemical 
extinguishers,  pails  of  sand,  automatic  sprinklers,  watchman 
service,  auxiliary  fire-alarm  service,  thermostats,  etc.  Again, 
credits  are  given  for  improvements  in  the  public  fire  protec¬ 
tion,  such  as  increased  water  supply,  increased  water 
pressure,  fire-boats,  additional  apparatus,  additional  firemen, 
additional  hydrants,  larger  water  mains,  approved  fire-alarm 
systems,  salvage  corps,  etc. 

27.  Until  the  great  majority  of  poorly  constructed  build¬ 
ings  that  predominate  everywhere  are  torn  down  and 


18 


INSURANCE  ENGINEERING 


42 


replaced  by  structures  that  are  more  nearly  fireproof,  the 
urgent  need  of  the  United  States  must  be  the  improvement 
of  faulty  construction  in  the  sections  of  cities  where  con¬ 
flagrations  are  liable  to  occur  any  day.  Schedule  rating  has 
shown  owners  and  occupants  of  buildings  how  certain  com¬ 
mon  defects  in  the  construction  of  buildings  favor  heavy 
losses  from  fire  and  the  approximate  cost  of  each  defect  in 
insurance  rates.  Schedule  rating  is  not  a  perfect  system  of 
arriving  at  adequate  rates,  but  it  is  a  vast  improvement  over 
the  old  method  of  guessing.  “A  system  of  insurance  rating 
which  does  not'  discriminate  between  safe  construction  and 
unsafe  construction,  and  between  carefulness  and  neglect,  is 
an  injury  to  the  community.” 


LIMITS  OF  INSURANCE 

28.  The  wasting  of  property  through  destruction  by  fire 
is  a  tax  on  capital,  and  so  are  insurance  premiums.  The 
modern  system  of  fire  insurance  distributes  about  65  per 
cent,  of  losses  on  the  general  public,  and  35  per  cent,  falls 
on  the  owners  individually.  In  other  words,  only  about 
65  per  cent,  of  losses  are  covered  by  insurance.  To  protect 
the  capital  that  is  invested  in  the  insurance  business  and  to 
pay  losses  in  full,  it  is  necessary  to  limit  the  amount  of 
insurance  written  on  any  building  and  in  a  certain  area  taken 
as  a  whole.  One  stock  fire-insurance  company  may  be  will¬ 
ing  to  write  a  policy  for  $10,000  on  a  certain  building, 
whereas  another  stock  company  may  feel  warranted  in 
writing  a  policy  for  only  $5,000,  and  so  on.  A  merchant 
requiring  $100,000  of  insurance  must,  in  order  to  cover  that 
amount,  get  enough  companies  to  insure  him. 

It  is  a  matter  of  public  record  that  thousands  of  firms  and 
individuals  are  unable,  every  year,  to  secure  all  the  insurance 
they  require  to  protect  their  credit.  To  be  underinsured  is 
to  face  the  most  serious  consequences  of  a  fire.  In  many 
cases  the  fact  that  a  merchant  or  a  manufacturer  cannot 
secure  enough  insurance,  means  that  the  fire  risk  of  his  store 


§42 


INSURANCE  ENGINEERING 


19 


or  his  mill  is  so  great  that  some  companies  will  write  only 
the  minimum  amount  and  others  will  write  nothing.  This 
situation  also  means  that  the  amount  of  insurance  to  be  had 
from  all  the  companies  in  the  world  is  decidedly  limited:  A 
general  conflagration  in  the  wholesale  and  retail  districts  of 
New  York  City — an  impending  calamity — would  more  than 
equal  the  loss-paying  ability  of  the  entire  insurance  system. 
There  is  not  enough  insurance  capital  to  provide  for  the 
losses  that  would  in  all  probability  occur  in  that  compara¬ 
tively  small  area.  The  fire-insurance  business  was  practically 
recapitalized  after  the  San  Francisco  conflagration. 

29.  The  greatest  protection  to  capital  and  credit  is  fire 
prevention  and  the  prevention  of  undue  losses  from  fire  by 
the  adoption  of  certain  simple  safeguards.  It  is  a  business 
proposition  for  individuals  and  for  municipalities.  Safe¬ 
guards  cost  money,  but  they  constitute  an  investment  in 
every  sense  of  the  word.  The  high-pressure  fire-main 
system  provided  by  the  city  of  Philadelphia  brought  about  a 
reduction  of  25  per  cent,  in  insurance  rates  on  property  in 
the  district  protected,  and,  further,  has  manifestly  brought 
about  a  material  reduction  in  the  yearly  fire  loss  in  that  city, 
even  in  spite  of  an  increased  number  of  fires. 

Whatever  is  done  to  prevent  loss  of  property  by  fire  must 
be  done  thoroughly,  or  the  money  invested  may  be  wasted. 

Thousands  of  fire-insurance  companies  have  disbanded 
because  the  business  was  unprofitable — not  a  few  have  been 
forced  out  of  existence  by  general  conflagrations. 

The(  man  who  cannot  shift  the  liability  of  loss  by  fire  on 
the  public  at  large,  through  the  operation  of  fire  insurance, 
must  insure  himself  in  a  very  true  sense.  This  means  that 
he  must  do  his  utmost  to  prevent  losses  from  fire — losses 
due  to  his  own  neglect  and  the  neglect  of  his  neighbor. 

The  results  of  insurance  engineering  as  practiced  by  the 
progressive  underwriters  of  today  bear  the  highest  testimony 
to  the  wisdom  of  fire  prevention. 


WATERPROOFING  OF  CONCRETE 


INTRODUCTION 


REQUIREMENTS  OF  WATERPROOFING 

1.  Water-Tightness  of  Concrete. — Concrete  may  be 
considered  at  first  thought  to  be  a  waterproof  material. 
Water  will  not  flow  through  it  with  a  great  degree  of 
rapidity,  and  it  may  even  be  used  for  dams  and  similar 
structures  where  water  must  be  held  back.  Yet,  strictly 
speaking,  concrete  is  not  waterproof.  Thin  concrete  walls  are 
liable  to  contain  small  fissures  that  will  permit  seepage;  also, 
they  are  almost  invariably  sufficiently  porous,  unless  special 
precautions  are  taken,  to  allow  the  penetration  of  dampness. 
The  same  facts  are  true,  though  in  a  less  degree,  of  mass¬ 
ive  concrete  walls.  Present  engineering  practice  regards  it 
as  essential  that  some  means  of  resisting  water  penetration 
be  provided  other  than  the  concrete  itself.  The  first  rein- 
forced-concrete  roofs  were  failures  until  they  were  provided 
with  additional  waterproofing,  and  although  many  basements 
and  foundations  have  been  built  of  concrete  or  of  masonry 
without  waterproofing,  there  has  frequently  been  difficulty  in 
keeping  them  free  from  water,  and  many  of  them  are  subject 
to  dampness.  The  same  remarks  apply  to  the  construction 
of  tunnels  and  subways. 

Ideas  about  the  necessity  of  waterproofing  have  changed 
greatly  in  the  last  few  years.  In  days  gone  by,  dampness 
was  ignored,  and  the  dripping  of  water  from  the  soffits  of 
arched  bridges  or  the  roofs  of  tunnels  was  considered  of 


COPYRIGHTED  BY  INTERNATIONAL  TEXTBOOK  COMPANY  ENTERED  AT  STATIONERS'  HALL,  LONDON 


22 


WATERPROOFING  OF  CONCRETE 


§42 


little  consequence.  Modern  requirements,  however,  in  the 
art  of  waterproofing  include  the  entire  exclusion  of  dampness 
as  well  as  actual  leakage. 

2.  Degree  of  Waterproofing. — The  term  waterproof¬ 
ing  as  applied  to  concrete  is  relative  rather  than  absolute. 
There  are  two  aspects  from  which  the  variation  of  the  term 
may  be  noted.  A  wall  of  a  culvert  or  of  a  sewer  may  be 
termed  waterproof  because  it  will  not  allow  any  large  amount 
of  water  to  percolate  through  it,  yet  this  same  wall  might 
readily  allow  dampness  to  penetrate  it,  and  while  suitable  for 
a  culvert,  it  would  be  entirely  unfit  for  a  cellar  wall.  Then, 
again,  a  wall  of,  say,  a  cellar  may  keep  back  moisture  and 
dampness  under  ordinary  conditions  because  the  water  pres¬ 
sure  on  the  outside  of  the  wall  is  slight;  but  if  this  same  wall 
were  near  the  bottom  of  a  tunnel  under  a  river,  it  would 
not  be  waterproof,  because  the  water  pressure  against  it 
would  be  very  much  increased.  A  structure,  therefore,  may 
be  called  waterproof  when  it  will  hold  back  the  required 
amount  of  water  under  the  required  conditions.  To  be 
absolutely  waterproof,  it  must  hold  back  all  moisture  under 
the  most  trying  conditions.  Of  course,  if  conditions  do  not 
require  a  Structure  to  be  absolutely  waterproof,  making  it  so 
would  be  only  a  waste  of  money. 

3.  Necessity  of  Waterproofing. — The  importance  of 
waterproofing  is  so  obvious  as  to  require  but  little  explana¬ 
tion.  Plaster  and  decorations  in  the  basements  of  buildings, 
especially  modern  office  buildings  in  large  cities,  must  be 
protected  from  moisture.  It  is,  of  course,  needless  to  call 
attention  to  the  great  necessity  of  waterproofing  structural 
steel  in  buildings  of  cage  construction.  Besides  the  necessity  of 
waterproofing  to  protect  the  materials  in  the  interior  of  a  build¬ 
ing,  so  as  to  prevent  their  deterioration,  waterproofing  affects 
in  an  important  degree  the  health  of  a  community.  Diseases 
that  thrive  in  damp  walls  and  pools  of  water  in  cellars  either 
disappear  or  are  greatly  reduced  when  waterproofing  is  used. 

In  former  times,  th'e  placing  of  cellars  under  houses  in  the 
city  of  New  Orleans  was  considered  impracticable,  because 


§42 


WATERPROOFING  OF  CONCRETE 


23 


they  would  soon  become  filled  with  water  owing  to  the  excess¬ 
ive  amount  of  moisture  contained  in  the  soil.  Now,  how¬ 
ever,  by  means  of  the  modern  systems  of  waterproofing,  cel¬ 
lars  in  New  Orleans  are  kept  as  dry  as  those  in  any  other  city. 

4.  In  addition  to  the  waterproofing  of  cellars,  it  is  neces¬ 
sary  in  many  instances  to  waterproof  sewers,  conduits,  tunnels, 
arched  bridges,  and  other  engineering  structures  made  of 
concrete.  As  an  example  of  the  necessity  of  waterproofing 
sewers,  figures  are  quoted  from  a  paper  read  by  Myron  H. 
Lewis,  C.  E.,  before  the  Municipal  Engineers  of  the  City  of 
New  York.  These  figures  show  the  leakage  of  ground  water 
into  sewers  in  various  localities,  and  are  as  follows:  Colum¬ 
bus,  Ohio,  100  to  300  per  cent,  of  dry- weather  flow;  Kalama¬ 
zoo,  Michigan,  20  per  cent,  of  capacity;  Norfolk,  Virginia,  60 
per  cent,  of  pumping;  and  East  Orange,  New  Jersey,  110  per 
cent,  of  dry-weather  flow.  These  figures  cannot  be  com¬ 
pared  with  one  another  because  most  of  them  are  only 
estimates  and  are  measured  in  different  ways.  Thus,  at 
Kalamazoo  the  leakage  is  given  as  a  per  cent,  of  the 
capacity  of  the  sewer,  while  in  Columbus  it  is  given  as  a 
per  cent,  of  the  dry- weather  flow  and  in  Norfolk  as  a  per 
cent,  of  the  pumping.  All  of  them,  however,  ^  show  that 
the  useful  capacity  of  a  sewer  is  very  much  decreased  by 

allowing  water  to  leak  into  it  from  outside. 

c 

CLASSIFICATION  OF  SYSTEMS 

5.  There  are  three  principal  methods,  or  systems, 
employed  in  the  waterproofing  of  concrete.  They  may  be 
termed  the  integral ,  the  superficial ,  and  the  membrane  method. 

The  integral  method  consists  in  adding  something  to  the 
concrete  when  it  is  placed,  or  in  mixing  the  concrete  in  cer¬ 
tain  proportions,  so  as  to  make  it  waterproof  throughout. 
The  superficial  method  consists  in  coating  the  concrete  with 
some  material  that  will  adhere  to  the  concrete  and  remain 
attached.  The  membrane  method  consists  in  putting  on 
the  concrete  a  coating  that  is  distinct  from  it.  While  the 
coating  may  adhere  to  the  concrete,  it  does  not  crack  when 


24 


WATERPROOFING  OF  CONCRETE 


§42 


the  concrete  cracks,  but  is  in  a  distinct  membrane  usually 
strengthened  by  felt  or  some  other  fiber  cloth. 

6.  Each  of  these  methods  has  its  advantages  and  dis¬ 
advantages.  For  instance,  it  is  impossible  to  use  the  integral 
method  to  rectify  the  seepage  of  water  after  a  building  is 
already  built.  In  both  the  integral  and  the  superficial 
method,  a  large  crack  in  the  concrete  will  spoil  the  water¬ 
proofing  effect  and  will  allow  water  to  enter.  Again,  in  both 
the  membrane  and  the  superficial  method,  care  must  be 
exercised  not  to  puncture  the  waterproof  coat. 

These  three  methods  of  waterproofing  are  closely  allied 
to  each  other.  For  example,  there  are  various  processes  of 
waterproofing  on  the  market  that  are  about  half  way  between 
two  of  the  methods.  Thus,  when  paraffin  is  applied  to  a 
concrete  surface  with  a  brush,  it  belongs  to  the  superficial 
method,  and  yet  the  paraffin  penetrates  the  concrete  so  far 
as  to  be  almost  classed  as  an  example  of  the  integral  method. 
Likewise,  some  paints  may  be  classed  as  belonging  to  the 
superficial  method,  and  yet  they  are  elastic  enough  to  bridge 
over  minute  cracks  that  may  develop  in  the  concrete. 

'7.  It  is  unfortunate  that  some  manufacturers  of  water¬ 
proof  compounds  make  such  extravagant  claims  for  their 
own  method  while  condemning  the  methods  of  others.  There 
are  so  many  methods  of  waterproofing  in  the  market  today 
that  the  inexperienced  engineer  is  likely  to  become  confused 
when  about  to  make  a  selection.  Therefore,  before  trying 
a  method  of  waterproofing  with  which  he  is  not  familiar,  the 
engineer  should  satisfy  himself,  both  by  laboratory  tests  and 
by  the  examination  of  buildings  that  have  been  made  water¬ 
proof  by  this  method,  that  the  system  under  consideration  is 
sufficient  and  will  fill  the  required  conditions. 

It  is  impossible  in  this  Section  to  describe  all  the  systems 
of  waterproofing  in  the  market.  There  are  a  number  of 
more  or  less  patented  or  secret  processes  that  have  been  used 
with  success.  Many  of  these,  however,  act  on  the  principles 
to  be  described  and  do  not  differ  from  each  other  and  from 
the  systems  given  to  a  very  great  extent. 


§42 


WATERPROOFING  OF  CONCRETE 


25 


WATERPROOFING  METHODS 


INTEGRAL  METHOD 


MIXING  OF  CONCRETE 

8.  According  to  some  authorities,  if  concrete  is  properly 
mixed,  it  will  be  impervious  to  water.  The  exact  mixture 
to  use  will  depend  on  the  quality  of  sand  and  broken  stone, 
and  it  is  only  by  experiment  with  the  same  quality  of  sand  and 
broken  stone  that  is  to  be  used  that  this  ideal  mixture  can 
be  arrived  at.  Of  course,  it  seems  hardly  necessary  to  say 
that  this  most  waterproof  mixture  is  also  the  densest  mixture. 
Therefore,  in  searching  for  the  most  waterproof  mixture  of 
concrete,  the  engineer  really  finds  the  densest  mixture. 
For  many  grades  of  sand  and  broken  stone,  a  1-1  ^-3  mixture 
is  used. 

To  be  impervious  to  water,  concrete  must  be  placed  in  a 
wet  condition  and  be  well  rammed  into  place.  If  the 
concrete  is  mixed  with  too  little  water,  it  cannot  be 
rammed  into  a  very  compact  mass  with  ordinary  ramming 
tools. 

Concrete,  particularly  that  which  is  very  dense,  becomes 
more  impervious  to  water  as  it  grows  older.  The  first  water 
that  penetrates  it  carries  particles  of  clay  and  other  material 
that  stop  up  its  pores  and  gradually  make  it  more  water¬ 
proof. 


9.  While  the  method  of  waterproofing  concrete  by  so 
proportioning  the  concrete  itself  that  it  is  impermeable 
would  appear  to  be  an  ideal  one,  yet  the  method  has  some 
bad  features.  In  the  first  place,  it  is  much  more  difficult 
to  proportion  the  concrete  carefully  in  field  work  than  it 


26 


WATERPROOFING  OF  CONCRETE 


§42 


is  in  the  laboratory;  and  while  samples  of  concrete  made 
in  the  laboratory  might  seem  impermeable,  it  is  doubt¬ 
ful  whether  the  same  concrete  would  also  seem  impermeable 
when  made  in  the  field.  Then,  again,  to  obtain  a  concrete 
that  is  entirely  impermeable,  it  must  be  made  fairly  rich. 
Under  these  conditions,  it  would  often  have  more  strength 
than  is  really  required;  that  is,  to  gain  waterproof  qualities, 
it  is  often  necessary  to  use  a  better  concrete  than  would 
otherwise  be  required.  Such  a  procedure,  of  course,  would 
not  be  economical. 

Concrete,  when  properly  mixed,  is  waterproof  only  up  to 
a  certain  degree.  If  the  water  is  under  great  pressure,  as  at 
the  bottom  of  very  deep  foundations  in  very  wet  soils,  it 
is  probable  that  moisture  will  gradually  soak  through  the 
concrete.  Another  objection  that  should  not  be  overlooked 
is  the  liability  of  the  concrete  to  crack.  While  this  danger 
is  under  control  today,  every  precaution  should  be  taken 
to  avoid  it. 


ADDING  OF  DIME  OR  CLAY 

10.  Hydrated  Lime. — By  hydrated  lime  is  meant 
lime  that  has  been  slaked  in  water.  It  can  be  bought  com¬ 
mercially  in  the  form  of  a  dry  powder.  For  the  water¬ 
proofing  of  concrete,  pqre  calcium  hydrate,  or  hydrated  lime, 
as  it  is  called,  must  be  added  to  the  cement.  It  should  be 
dried  and  pulverized,  however,  before  adding  it  to  the  cement, 
and  in  slaking  it  must  be  thoroughly  mixed  with  the  water 
in  order  that  no  unslaked  lumps  will  remain.  Too  much 
water  must  not  be  used  in  slaking,  as  the  extra  water  is 
difficult  to  remove  and  some  of  the  lime  is  liable  to  be  dete¬ 
riorated  by  it.  At  present,  few  contractors  slake  their  own 
lime,  because  lime  slaked  by  special  machinery,  reduced  to  a 
fine  powder,  and  packed  in  bags,  can  be  bought  in  the  market. 

11.  The  purpose  of  adding  hydrated  lime  to  concrete  is  to 
fill  mechanically  the  voids  in  the  latter.  The  lime  possesses 
the  property  of  coating  each  particle  of  sand  and  filling  up 
all  the  voids  around  it. 


WATERPROOFING  OF  CONCRETE 


27 


§42 

Hydrated  lime  is  a  white,  soft-feeling,  smooth  powder  that 
is  light  in  weight.  For  equal  weights,  it  occupies  about 
two  and  one-half  times  the  bulk  of  cement.  The  results  of 
various  experiments  differ  as  to  how  much  hydrated  lime 
affects  the  strength  of  the  concrete,  but  it  is  generally  con¬ 
sidered  that  the  decrease  in  strength  is  slight. 

12.  If  good  results  are  to  be  obtained  with  the  use  of 
hydrated  lime,  it  must  be  mixed  thoroughly  with  the  dry 
cement.  After  the  cement  and  lime  are  mixed  until  the  color 
of  the  mixture  is  uniform,  the  sand,  broken  stone,  and  water 
are  added  as  usual.  The  concrete  should  be  made  wet,  and 
great  care  must  be  exercised  in  bonding  old  and  new  work. 

Hydrated  lime  is  intended  to  assist  in  making  the  con¬ 
crete  waterproof.  It  must  not  be  thought  that  by  adding 
hydrated  lime  all  care  as  to  the  mixing  of  concrete,  the 
amount  of  water  used,  and  the  placing  of  the  concrete  may 
be  dispensed  with.  These  precautions  must  be  taken  just 
the  same  as  if  the  hydrated  lime  were  not  added. 

13.  The  amount  of  hydrated  lime  to  be  added  to  make 
concrete  waterproof  depends  on  many  factors.  If  fine  sand 
is  to  be  used  instead  of  coarse  sand,  a  smaller  quantity  of 
lime  will  be  required.  The  amount  of  lime  to  be  employed 
is  usually  given  as  a  percentage,  by  weight,  of  the  cement. 
Under  ordinary  conditions,  for  1-2-4  concrete,  8  per  cent,  of 
lime  will  be  found  sufficient,  and  for  1-3-6  concrete,  17  per 
cent,  of  lime  will  be  required.  If  possible,  a  good  plan  is  to 
test  the  permeability  of  the  concrete  that  it  is  intended  to 
use  on  a  certain  structure  with  various  percentages  of  lime 
before  the  work  is  started. 

For  very  rich  mixtures  of  concrete,  when  hydrated  lime  is 
to  be  added,  it  is  well  to  reduce  the  amount  of  cement 
employed;  that  is,  with  rich  mixtures,  instead  of  adding  the 
lime  as  in  ordinary  mixtures,  it  is  better  to  substitute  the 
lime  for  part  of  the  weight  of  cement. 

Hydrated  lime  forms  an  efficient  means  of  waterproofing 
concrete  under  all  ordinary  conditions.  The  two  most 
important  details  to  be  looked  after  when  using  hydrated 
211— 3S 


28 


WATERPROOFING  OF  CONCRETE 


§42 


lime  are  the  careful  mixing  of  the  concrete  and  the  intro¬ 
duction  of  steel  or  the  use  of  some  other  precaution  to  prevent 
cracks  in  the  concrete  after  it  has  set. 

14.  Collodial  Clay. — In  place  of  hydrated  lime,  con¬ 
crete  is  often  waterproofed  by  mixing  with  it  finely  ground 
collodial  clay.  This  clay  acts  in  the  same  manner  as  the 
lime  and  is  simply  a  void  filler.  It  is  recommended  that 
clay  equal  to  about  10  per  cent,  of  the  weight  of  the  cement 
be  used  in  a  mixture.  The  clay  must  be  thoroughly  dry  and 
well  mixed  with  the  cement.  If  this  precaution  is  not  taken, 
the  clay  is  liable  to  roll  up  into  little  balls. 


SYLVESTER  PROCESS 

15.  The  Sylvester  process  of  waterproofing  concrete 
is  an  old  one,  but  it  has  proved  successful  on  many  occasions. 
It  consists  in  adding  powdered  alum  and  soft  soap  to  the 
concrete.  The  alum  and  soft  soap  combine  chemically  to 
form  alumina  and  fatty  acids.  The  compounds  are  insoluble 
in  water,  and  they  fill  up  the  voids  in  the  concrete  with  an 
insoluble,  gelatinous  mass. 

In  using  the  Sylvester  process,  first  the  sand  and  cement 
are  mixed  together  dry,  as  usual.  To  this  mixture  is  added 
alum  equal  to  1  per  cent,  of  the  weight  of  the  mixture.  To 
the  water  to  be  used  is  added  1  per  cent.,  by  weight,  of 
soft  soap,  and  this  soap  is  then  thoroughly  dissolved.  The 
mortar  is  made  wet,  and  the  broken  stone  is  added  in  the 
usual  manner.  Ordinary  precautions  should  be  taken  to 
make  the  concrete  dense,  and  as  a  rule  it  is  mixed  rather  wet. 


METALLIC  STEARATES  AND  OTHER  COMPOUNDS 

16.  Besides  the  materials  mentioned,  various  other 
chemicals  are  used  to  make  concrete  waterproof.  One  of 
the  most  successful  of  these  is  calcium  stearate,  which  is 
a  salt  of  a  fatty  acid.  Calcium  stearate  fills  the  pores  of 
the  cement  and  in  addition  has  the  power  to  repel  water. 


§42 


WATERPROOFING  OF  CONCRETE 


29 


Usually,  the  quantity  of  finely  ground  metallic  stearate 
added  to  the  cement  to  make  the  concrete  waterproof  is 
about  2  per  cent,  of  the  weight  of  the  cement.  This  material 
is  the  base  of  many  well-known  commercial  waterproofing 
compounds,  and  is  usually  bought  under  trade  names. 

17.  Besides  the  metallic  stearates,  other  substances  are 
used  more  or  less  to  waterproof  concrete  by  the  integral 
method.  A  mixture  of  oil  and  water  has  been  used  with 
success,  as  has  also  chloride  of  lime.  The  purpose  of  the 
chemicals  is  usually  to  fill  the  voids,  and,  in  addition,  some 
of  them  are  water  repellants. 


SUPERFICIAL  METHOD 


PAINT 

18.  If  a  cement  wall  leaks  after  it  is  built,  it  cannot  be 
repaired  by  the  integral  method.  It  must  therefore  be 
repaired  by  either  the  superficial  or  the  membrane  method. 
It  is  always  better,  if  possible,  to  put  the  superficial  coat  on 
the  side  of  the  wall  against  which  the  water  presses.  This 
pressure  then  has  a  tendency  to  hold  the  waterproof  coat  in 
place.  If  the  coat  cannot  be  put  on  the  water  side  of  the 
wall,  it  must  then  be  placed  on  the  other  side.  As  this  is 
the  side  that  is  usually  most  easily  accessible,  many  inventors 
have  endeavored  to  obtain  a  coating  that  can  be  success¬ 
fully  put  on  this  side  of  a  structure. 

19.  There  are  many  patented  waterproof  paints  on  the 
market  that  may  be  used  to  paint  walls  on  the  inside,  pro¬ 
vided  the  water  pressure  is  not  too  great.  It  is  impossible 
to  give  a  complete  list  of  all  of  them,  however,  as  new  ones 
are  being  continually  manufactured.  If  the  wall  develops 
no  large  cracks,  many  of  these  paints  will  prove  to  be  very 
satisfactory. 

One  of  the  best  known  of  these  paints  is  Toeli’s  It.  I.  W. 
It  is  very  effective  as  a  waterproof  coating  if  used  according  to 


30 


WATERPROOFING  OF  CONCRETE 


§42 


directions.  It  sticks  to  the  concrete  wall  and  will  not  stain 
stonework.  Different  grades  are  made  to  be  used  for  various 
purposes  and  in  various  locations. 

Another  serviceable  paint  for  concrete  is  elaterite.  It  can 
be  painted  on  the  concrete,  and  plaster  may  then  be  put 
directly  on  top  of  it.  It  is  somewhat  elastic  and  forms  a  film 
over  the  concrete,  so  that  hair  cracks  may  develop  in  the  latter 
without  causing  the  paint  surface  to  open. 

There  are  other  waterproof  paints  in  the  market  having 
about  the  same  properties  as  the  two  just  mentioned,  and 
they  are  useful  for  the  same  purposes. 


WAXES 

20.  To  make  concrete  waterproof,  it  is  sometimes  coated 
with  wax.  The  wax  sinks  into  the  pores  of  the  concrete, 
filling  the  voids  therein  and  thus  preventing  the  percolation 
of  water. 

21.  Paraffin  is  used  for  waterproofing  with  considerable 
success.  A  paraffin  especially  hardened  to  resist  the  sun’s 
rays  is  used.  The  concrete  surface  on  which  the  paraffin  is  to 
be  applied  should  be  thoroughly  dry  and  not  very  cold.  In 
fact,  it  is  better  to  warm  the  surface  with  a  torch  if  possible. 
The  paraffin  is  heated  and  then  applied  with  a  brush.  The  hot 
paraffin  is  absorbed  by  the  concrete,  into  which  it  penetrates 
for  a  short  distance.  Paraffin  will  resist  the  action  of  acids 
and  alkalies.  The  treatment  just  described  has  been  found 
very  effective. 

Instead  of  applying  paraffin  while  hot,  it  may  be  dissolved 
in  some  volatile  carrier,  such  as  benzine.  The  dry  wall  is 
painted  with  this  solution,  which  is  readily  absorbed.  The 
carrier  then  evaporates  and  leaves  the  paraffin  to  fill  the  pores 
in  the  surface  of  the  wall.  If  the  carrier  is  inflammable,  care 
must  be  taken  in  using  it. 

22.  There  is  now  in  the  market  an  effective  waterproofing 
material  known  as  Minwax.  It  is  a  mineral  product  and 
contains  ozocerite,  which,  although  a  mineral,  is  a  near 


WATERPROOFING  OF  CONCRETE 


31 


§42 

approach  to  beeswax.  Minwax  is  not  affected  by  acids  and 
alkalies  and  is  manufactured  in  various  forms.  Probably 
the  best  form  to  use  is  the  liquid,  which  may  be  applied  to 
the  concrete  with  a  brush,  the  same  as  paint.  Minwax  has 
been  successfully  used  to  render  concrete  waterproof. 


CEMENTS 

23.  One  method  of  waterproofing  concrete  that  is  popular 
is  to  coat  the  surface  of  the  concrete  with  an  impervious 
cement  coating.  Sometimes  this  coating  is  simply  a  rich, 
dense  cement  mortar,  sometimes  it  contains  a  waterproofing 
compound  similar  to  those  mentioned  in  connection  with  the 
integral  method,  and  sometimes  a  special  waterproof  cement 
is  used. 

There  are  three  features  that  must  be  carefully  considered 
in  waterproofing  by  means  of  cement:  (1)  The  cement 
coating  itself  must  be  waterproof;  (2)  the  engineer  must 
satisfy  himself  that  the  walls  upon  which  the  cement  coating 
is  to  be  placed  will  not  crack;  and  (3)  the  coating  must 
adhere  strongly  to  the  wall. 

To  insure  that  the  coating  will  be  waterproof,  a  proper 
mixture  of  reliable  materials  must  be  used.  Often,  the 
structure  is  built  before  the  waterproofing  problem  has  been 
taken  up.  If  there  is  any  likelihood  of  the  walls  ever  cracking, 
it  is  useless  to  try  to  waterproof  them  with  an  ordinary  cement 
coating,  because  this  will  crack  also;  but  if  the  building  has 
been  built  properly,  the  coating  of  cement  should  be  effective. 

The  third  consideration,  namely,  the  adhesion  between  the 
coating  and  the  concrete  work,  requires  the  most  careful 
consideration.  The  concrete  surface  on  which  the  water¬ 
proof  coating  is  to  be  placed  must  first  be  chipped  and 
scraped  to  remove  all  glaze  and  to  obtain  a  rough  texture. 
The  surface  must  then  be  washed  thoroughly  with  clean 
water  to  remove  all  dust,  and  all  cracks  must  be  filled  with 
mortar.  While  the  surface  is  still  wet,  it  is  painted  with  a 
mixture  of  cement  and  water  of  about  the  consistency  of 
thick  cream.  This  mixture  is  applied  with  a  stiff  brush  and 


32 


WATERPROOFING  OF  CONCRETE 


§42 


must  be  rubbed  well  into  the  surface.  Before  this  coat  dries 
the  first  coat  of  waterproof  mortar  is  put  on,  usually  about 
\  inch  thick.  This  coat  must  be  troweled  into  the  surface 
with  great  care.  Then,  before  this  coat  sets,  another  coat  of 
waterproof  mortar  of  about  the  same  thickness  or  a  little 
thicker  is  applied. 

The  successful  way  of  making  cement  coatings  stick  is  to 
have  the  concrete  surface  very  rough  and  clean  and  wet,  and 
then  to  put  on  each  coat  before  the  preceding  one  has  had 
time  to  dry  or  set. 


BITUMINOUS  COATINGS 

24.  Besides  many  specially  prepared  bituminous  com¬ 
pounds  sold  under  trade  names,  asphalt  and  coal  tar  are  used 
for  waterproofing  by  what  may  be  classed  as  the  superficial 
method.  It  is  sometimes  recommended  that  the  surface  to 
be  waterproofed  should  be  treated  with  a  preliminary  appli¬ 
cation  of  dead  oil.  The  material  is  then  applied  hot  with  a 
mop.  Several  coatings  are  usually  employed.  If  a  very 
thick  coat  is  placed  on  a  vertical  surface,  heat  is  liable  to 
make  it  run  unless  it  is  supported  in  some  way.  Coal  tar  or 
asphalt  is  therefore  often  used  in  connection  with  a  cloth 
fabric,  as  will  be  explained  under  the  membrane  method. 


MEMBRANE  METHOD 


MANUFACTURED  MEMBRANES 

25.  There  are  in  the  market  some  excellent  waterproofing 
fabrics  and  ready-made  roofings.  It  is  impossible  to  describe 
here  the  method  of  using  these  various  fabrics.  They  are 
used  in  different  ways,  and  should  be  placed  according  to  the 
directions  of  their  manufacturers.  They  should  be  purchased 
only  from  reliable  concerns  who  have  had  success  with  their 
product  under  conditions  similar  to  those  which  are  to  be 
encountered. 


§  42  WATERPROOFING  OF  CONCRETE 


33 


One  of  the  most  popular  and  satisfactory  methods  of 
waterproofing  is  the  bituminous  membrane  that  is  built 
into  place  piece  by  piece.  It  is  proposed  to  devote  the  remain¬ 
der  of  this  Section  to  the  description  and  use  of  this  method, 
as  the  materials  for  it  can  be  purchased  anywhere  and  need 
not  be  obtained  from  just  one  manufacturer. 


BITUMINOUS  MEMBRANES 

26.  The  common  bituminous-membrane  method  consists 
in  the  use  of  a  felt  saturated  with  bituminous  material  and 
a  bituminous  binder.  By  a  binder ,  as  the  word  would  imply, 
is  meant  a  material  that  binds  two  surfaces  together;  that  is, 
an  adhesive  material.  By  a  bituminous  material  is  meant 
any  material  containing  a  large  proportion  of  solid  or  semi¬ 
solid  bitumen,  bitumen  being  that  portion  of  pitch  that  is 
soluble  in  carbon  bisulphide,  benzol,  petroleum,  ether,  or 
other  similar  solvent. 

The  bituminous  membrane  is  built  up  in  place  in  successive 
layers,  and  should  form,  when  finished,  a  practically  homoge¬ 
neous  and  continuous  waterproof  envelope.  The  functions 
of  the  saturated  felt  and  bituminous  binder  should  be  clearly 
understood.  The  use  of  the  felt  is  to  serve  as  a  retainer  of 
the  pitch  or  bitumen;  that  is,  the  felt  serves  to  hold  the 
bitumen  in  place,  while  the  latter  is  the  waterproofing 
material.  Even  though  pitch  or  bitumen  appears  hard  at 
ordinary  temperatures,  it  is  somewhat  viscous  and  has  the 
property  of  flowing  under  moderate  but  continued  pressure. 
This  tendency  to  flow  is  counteracted  by  using  it  in  thin 
layers  between  successive  courses  of  absorbent  felt.  The 
pitch  penetrates  the  felt  and  the  felt  serves  to  hold  the  pitch 
in  place  and  to  give  strength,  very  much  as  does  the  hair 
used  in  mortar.  The  felt  also  enables  the  pitch  to  resist 
ordinary  pressure  and  to  bridge  small  fissures  caused  by 
settlement.  The  felt  is  therefore  an  essential  part  of  the  com¬ 
bination,  but,  as  should  be  understood  clearly,  it  is  not  in  itself 
the  waterproofing  material,  and  must  at  all  times  be  com¬ 
pletely  enclosed  and  protected  by  an  unbroken  layer  of  pitch. 


34 


WATERPROOFING  OF  CONCRETE 


§42 


27.  Coke  is  a  fuel  used  largely  in  blast  furnaces.  It  is 
made  by  heating  soft  coal.  Coke  bears  the  same  relation  to 
coal  as  charcoal  does  to  wood.  In  the  manufacture  of  coke, 
the  heat  drives  gases  out  of  the  coal  and,  at  the  same  time, 
a  black,  viscous  bituminous  material  is  obtained  from  the 
coal,  leaving  the  coke.  This  material  is  coal  tar,  so  useful 
in  manufacturing  and  waterproofing. 

28.  Asphalt,  or  asphaltiim ,  as  it  is  sometimes  called, 
is  a  natural  bituminous  material  found  in  various  parts  of 
the  world  in  a  more  or  less  advanced  state  of  distillation. 
The  asphalt  commonly  used  in  America  is  obtained  either 
from  Trinidad  or  from  Bermudes.  That  obtained  from 
the  former  place  is  known  as  Trinidad ■  pitch-lake  asphalt , 
and  that  from  the  latter  place  as  Venezuelan  asphalt .  Asphalt 
is  also  found  in  some  parts  of  the  United  States. 

29.  The  exact  meaning  of  the  term  pitch  should  be 
understood,  so  as  to  remove  some  widespread  misconcep¬ 
tions.  Pitch  is  a  general  term,  and  it  may  be  applied  indis¬ 
criminately  to  coal  tar,  and  also  to  the  resinous  sap  of  pine 
trees,  or  to  asphalt. 

All  kinds  of  pitch  have  in  common  the  property  of  resist¬ 
ing  the  penetration  of  water,  although  in  a  greater  or  less 
degree,  so  that  the  name  itself  has  become  synonymous  with 
the  waterproofing  quality. 

30.  Qualities  of  Pitch. — In  purchasing  pitch  or  bitu¬ 
minous  waterproofing,  only  trustworthy  companies  should  be 
allowed  to  bid,  as  it  is  of  the  utmost  importance  to  obtain 
first-class  material.  Good  waterproofing  cannot  be  made 
from  poor  pitch.  The  source  of  the  pitch  or  bituminous 
binder  is  a  question  of  great  importance,  because  on  its 
ability  to  resist  the  dissolving  action  of  water  rests  the  per¬ 
manence  bf  its  waterproofing  effect.  In  underground  work, 
the  action  of  the  water  is  sometimes  made  more  difficult  to 
resist  because  it  contains  sewage,  drainage  from  manufactur¬ 
ing  establishments,  gas  liquor,  etc.,  which  have  a  solvent 
action  on  poor  pitch.  On  a  roof,  it  is  not  only  the  dissolving 


§42 


WATERPROOFING  OF  CONCRETE 


35 


action  of  water,  but  also  the  effects  of  sun  and  wind,  heat 
and  cold,  that  must  be  withstood.  The  corroding  influence 
of  these  agencies  is  so  strong  that  few  materials  can  resist 
it  for  longer  than  a  few  years. 

The  pitch  binders  generally  used  in  bituminous  water¬ 
proofing  are  either  coal  tar  or  asphalt.  The  basis  of  either 
of  these  materials  is  bitumen,  and  they  differ  from  each  other 
in  the  amount  and  character  of  the  other  ingredients  present, 
corresponding  to  the  sources  from  which  they  are  derived. 
Crude  coal  tar  and  asphalt  are  put  through  a  process  of 
manufacture  or  refining  before  they  are  used  for  waterproof¬ 
ing  purposes. 

31.  Saturated  Felt. — As  its  name  implies,  saturated 
felt  is  nothing  more  nor  less  than  an  absorbent  felt  that  has 
been  passed  through  a  hot  bath  of  liquid  refined  tar  or  pre¬ 
pared  asphalt  of  such  consistency  as  to  penetrate  its 
structure  thoroughly,  superfluous  pitch  being  squeezed  out 
between  rollers.  After  this  treatment  the  felt  is  subjected  to 
an  aging  process,  which  toughens  it  and  makes  it  ready  for 
use.  It  is  of  course  essential  that  the  bituminous  binder 
and  the  saturating  material  with  which  the  felt  is  prepared 
should  be  similar  in  character,  in  order  that  the  union 
between  the  felt  and  the  pitch  binder  will  be  as  intimate 
as  possible. 


ROOF  WATERPROOFING 

32.  In  the  case  of  a  roof,  the  layers  of  felt  and  pitch  are 
often  covered  with  a  coat  of  gravel  or  slag  embedded  in  pitch. 
This  coating  serves  a  double  purpose,  first,  that  of  furnishing 
as  large  an  amount  of  mineral  surface  to  withstand  the  action 
of  the  elements  as  possible,  and  second,  to  stiffen  mechanic¬ 
ally  the  layer  of  pitch  and  prevent  it  from  flowing,  thereby 
making  it  possible  to  maintain  a  thicker  layer  in  place  on  the 
slope  of  the  roof  than  would  otherwise  be  the  case.  A 
gravel  or  a  slag  layer  also  serves  another  purpose,  namely, 
that  of  a  fire  retardant  of  no  mean  efficiency,  the  particles  of 


3G 


WATERPROOFING  OF  CONCRETE 


§42 


stone  serving  as  an  insulating  layer  and  protecting  the  pitch 
and  felt  from  the  action  of  sparks  or  embers.  A  roof  covered 
with  pitch  and  felt,  on  top  of  which  is  placed  slag  or  gravel,  is 
practically  as  uninflammable  as  one  covered  with  tin  or  tile. 

33.  Specifications  for  Coal-Tar  Pitch  and  Felt 
Roof  Over  Concrete. — The  following  specifications,  known 
as  Barrett  specifications ,  will  be  found  excellent  for  placing  a 
coal-tar  pitch  and  felt  roof  over  concrete.  Following  the 

specifications  are  data 
concerning  estima¬ 
ting,  flashings,  expan¬ 
sion  joints,  etc.  rec¬ 
ommended  by  the 
same  company. 

There  shall  be  used 
five  thicknesses  of  ap¬ 
proved  felt  weighing  not 
less  than  14  pounds  per 
100  square  feet,  single 
thickness,  not  less  than 
200  pounds  of  approved 
pitch,  and  not  less  than 
400  pounds  of  gravel  or 
300  pounds  of  slag  from 
\  to  -§  inch  in  size,  free 
from  dirt,  per  100  square 
feet  of  completed  roof. 

The  material  shall  be 
applied  as  follows:  (1) 
Coat  the  concrete  a,  Fig. 
1 ,  with  hot  pitch  b 
mopped  on  uniformly. 
(2)  Lay  two  full  thick¬ 
nesses  of  tarred  felt  c,  lapping  each  sheet  17  inches  over  the  pre¬ 
ceding  one,  and  mop  with  hot  pitch  d  the  full  width  of  the  17-inch  lap, 
so  that  in  no  case  shall  felt  touch  felt.  (3)  Coat  the  entire  surface 
with  hot  pitch  e  mopped  on  uniformly.  (4)  Lay  three  full  thicknesses 
of  felt  /,  lapping  each  sheet  22  inches  over  the  preceding  one  and 
mopping  with  hot  pitch  g  the  full  width  of  the  22-inch  lap  between  the 
plies,  so  that  in  no  case  shall  felt  touch  felt.  (5)  Spread  over  the 
entire  surface  of  the  roof  a  uniform  coat  of  pitch,  into  which,  while 


Fig.  1 


§42 


WATERPROOFING  OF  CONCRETE 


37 


hot,  embed  the  gravel  or  slag  h.  The  gravel  or  slag  in  all  cases  must 
be  dry. 

Note. — The  preceding  specifications  are  designed  for  roofs  having  an  incline  not 
exceeding  1  inch  to  the  foot,  and  by  adding  the  words  “such  nailing  as  is  necessary 
shall  be  done  so  that  all  naiis  will  be  covered  by  at  least  two  plies  of  felt,  ”  the  specifi¬ 
cations  are  suitable  for  inclines  not  exceeding  3  inches  to  the  foot.  For  surfaces 
steeper  than  3  inches  to  the  foot,  nailing  strips  of  wood  must  be  provided.  These  should 
be  embedded  in  the  concrete  from  3  to  6  feet  apart,  running  at  right  angles  to  the  pitch  of 
the  roof,  and  the  felt  nailed  to  these  strips. 

34.  Roof  Covered  With  Tile  or  Brick. — A  roof  laid 
in  accordance  with  the  preceding  specifications  will  resist  the 
action  of  the  elements  without  necessity  for  repair  for  many 
years.  Such  a  roof,  however,  is  not  calculated  to  withstand 
abrasion  or  traffic.  Where  it  is  necessary  for  persons  to 
walk  on  a  roof,  the  fabric  should  be  protected  from  injury 
by  a  layer  of  vitrified  tile  or  brick.  This  quality  of  roof  is 
the  one  generally  used  on  large  and  important  buildings  of 
the  first  class,  and  on  roof  gardens,  docks,  vaults,  and  places 
of  similar  character.  The  following  are  the  specifications  for 
this  type  of  work: 

Over  the  concrete  shall  be  laid  a  five-ply  coal-tar  pitch  felt  and 
vitrified  tile  or  brick  roof  to  be  constructed  as  folfows: 

The  tarred  felt  shall  be  of  approved  quality  weighing  not  less  than 
14  pounds  per  100  square  feet,  single  thickness. 

The  pitch  shall  be  approved  coal-tar  pitch,  distilled  direct  from 
American  coal  tar,  and  there  shall  be  used  not  less  than  200  pounds, 
gross  weight,  per  100  square  feet  of  completed  roof. 

The  material  shall  be  applied  as  follows:  First,  coat  the  concrete 
with  hot  pitch  mopped  on  uniformly.  Over  this  coating  of  pitch  lay 
two  thicknesses  of  tarred  felt,  lapping  each  sheet  17  inches  over  the 
preceding  one  and  mopping  back  with  pitch  the  full  width  of  each 
lap.  Over  the  felt  thus  laid,  spread  a  uniform  coating  of  pitch  mopped 
on.  Then  lay  three  full  thicknesses  of  tarred  felt,  lapping  each  sheet 
22  inches  over  the  preceding  one.  When  the  felt  is  thus  laid,  mop 
back  with  pitch  the  full  width  of  22  inches  under  each  lap.  Then  coat 
the  entire  surface  with  pitch  uniformly  mopped  on  and  finish  with  a 
course  of  vitrified-clay  tiles  6  in.  X  9  in.  X  1  in.  laid  in  and  thoroughly 
grouted  with  Portland-cement  mortar. 

Note. — The  same  general  specifications  apply  where  bricks  arc  used  instead  of  vitrified- 
clay  tiles. 

35.  Bata  for  Estimating. — For  convenience  in  esti¬ 
mating  the  quantity  of  felt  and  pitch  required  for  work 
according  to  the  preceding  and  following  specifications,  the 
following  data  are  given: 


38 


WATERPROOFING  OF  CONCRETE 


§42 


Standard  saturated  felt  is  32  inches  wide  and  weighs  from 
60  to  65  pounds  to  the  roll.  One  roll  contains  sufficient  felt 
for  four  squares  of  single-ply  waterproofing,  allowing  for 
the  laps. 

Standard  roofing  coal-tar  pitch  weighs  11  pounds  to  the 
gallon,  or  180  gallons  to  the  ton.  A  cement  barrel  of  pitch 
weighs  about  300  pounds.  For  one  square  of  roof  or  hori¬ 
zontal  waterproofing,  allow  40  pounds  of  pitch  for  each 
mopping.  For  one  square  of  wall  or  vertical  waterproofing, 
allow  50  pounds  of  pitch  for  each  mopping.  One  square  is 


equal  to  100  square 
feet,  or  10  ft.  X  10  ft. 


36.  Flashings. 

The  connections  be¬ 
tween  the  flat  sur¬ 
face  of  the  roof  and 
the  adjacent  parapet 
walls,  chimneys,  sky¬ 
light  and  scuttle 
curbs,  etc.  are  termed 
flashings.  Their 
object  is  to  prevent 
any  water  from  pene¬ 
trating  the  joint 


Fig.  2 


between  the  roof  and  the  vertical  surface.  The  material 
generally  used  is  metal,  either  sheet  copper,  zinc,  or  galvanized 
iron,  these  materials  being  named  in  the  order  of  merit,  as 
well  as  of  cost.  The  flashings  for  roofs  laid  with  gravel 
or  slag,  or  tile  or  brick,  are  practically  the  same;  there¬ 
fore,  in  Figs.  2  and  3,  the  finishing  course  of  vitrified  brick 
or  tiling  is  shown,  and  may  replace  the  gravel  or  slag 
coating  in  the  ordinary  type  of  construction. 

37.  Fig.  2  shows  a  flashing  laid  without  nails  over  con¬ 
crete.  The  bottom  flashing  of  copper,  zinc,  or  galvanized 
iron  is  4  inches  on  the  roof,  and  extends  up  8  inches  along 
the  side  of  the  wall,  with  a  counterflashing  extending  down 
4  inches  on  the  bottom  flashing  and  2  inches  into  the  wall. 


§42 


WATERPROOFING  OF  CONCRETE 


39 


•Y'<T  •  W-.<7v'-T 

S.-'&r&cxV 


The  counterflashing  is  built  in  at  the  time  the  wall  is  con¬ 
structed.  Before  the  tile,  brick,  gravel,  or  slag  is  laid  over 
the  lower  member  of  the  flashing,  a  binder  strip  of  felt  6  inches 
wide  and  cemented 
in  with  hot  pitch  is 
placed  over  the  flash¬ 
ing. 

38.  Fig.  3  shows 
the  method  of  build¬ 
ing  a  concrete  wall 
when  the  flashing  is  to 
be  put  in  after  the 
wall  is  built.  Provi¬ 
sion  for  the  counter-, 
flashing  is  made  by  a 
wooden  wedge  built  into  the  wall ;  the  wedge  is  to  be  removed 
before  the  counterflashing  is  placed.  In  this  case  the  flash¬ 
ing  extends  only  1  inch  into  the  wall.  When  this  provision 
is  made  in  concrete  for  placing  the  flashings,  the  joint  must 
be  pointed  with  either  paint  skins  or  pointing  cement.  The 
wooden  wedge  to  be  inserted  into  the  wall  while  building 
is  1  inch  wide  and  J  inch  thick  at  the  face  and  is  beveled 
back  to  a  thickness  of  J  inch  at  the  inner  edge.  Before 
being  placed  in  the  wall,  the  wedge  should  be  well  soaked 

in  water,  so  that  while 
the  concrete  is  drying  it 
will  shrink  and  be  easily 
removed.  If  placed  dry, 
it  will  absorb  moisture 
from  the  concrete  and  be 
almost  impossible  to 
remove. 


31).  Where  the  edge 
of  the  roof  that  is  to  be 
covered  with  gravel  or  slag  is  not  finished  with  gutters  or  para¬ 
pet  walls,  the  best  practice  calls  for  a  metal  strip,  either  of  cop¬ 
per,  zinc,  or  galvanized  iron,  formed  as  shown  in  Fig.  4.  The 


40 


WATERPROOFING  OF  CONCRETE 


§42 


inner  flange  is  nailed  to  the  concrete  on  top  of  the  two  lower 
plies  of  felt,  and  over  it  the  remaining  plies  of  felt  are  stuck. 
The  outward  flange  or  face  may  be  of  any  width  or  shape  to 
form  a  perfect  drip  from  the  fascia. 

40.  Expansion  Joint  of  Vitrified-Tile  or  Brick 
Roof. — A  vitrified  tile  or  brick  roof  laid  over  a  waterproofing 
course  of  pitch  and  felt,  as  in  the  preceding  specifications,  is 
subject  to  the  extremes  of  heat  and  cold,  and  inevitably 
expands  and  contracts.  Where  the  space  exposed  is  of 
small  dimensions,  sufficient  allowance  can  be  made  by  keep¬ 
ing  the  brick  or  tile  along  the  confining  walls  away  from  them 


Fig.  5 


i  inch  or  so  and  keeping  this  space  free,  to  be  taken  up  when 
the  expansion  occurs.  This  expedient  only  serves  for  dis¬ 
tances  up  to  25  feet,  however.  For  larger  areas,  a  special 
expansion  joint  is  recommended.  Expansion  joints  are 
always  made  of  copper,  and  when  designed  as  shown  in  Fig.  5 
have  been  found  to  give  excellent  service. 

41.  Fig.  5  shows  this  form  of  joint  in  place  in  the  roof. 
The  material  is  20-ounce  cold-rolled  sheet  copper,  which  is 
formed,  all  in  one  piece,  of  lengths  convenient  to  handle  or 
to  the  exact  dimensions  required.  On-  each  section,  the 
sheet  along  the  line  a  b  is  so  cut  as  to  project  4  inch  beyond 


WATERPROOFING  OF  CONCRETE 


41 


§  42 

the  remainder  of  the  form,  and  when  successive  sections  are 
placed  together,  this  lap  fits  over  the  next  section  and  is 
soldered  to  it.  The  only  soldering  is  done  on  this  line. 

The  expansion  joint  is  located  either  in  the  valley  or  on 
the  ridge  of  the  roof,  according  to  the  design.  It  will  take 
care  of  the  expansion  of  from  25  to  50  feet  of  brick  or  tile 
on  either  side;  that  is,  it  will  suffice  for  a  space  100  feet  wide 
if  placed  on  the  middle  line.  However,  as  the  ridges  and 
valleys  are  the  natural  places  for  an  expansion  joint,  it  is 
usually  placed  with  reference  to  them. 

In  laying  the  expansion  joint  in  place,  a  guide  stick  1  in. 
X  1  in.  and  about  2j  feet  long  is  used  to  keep  the  brick 
or  tile  at  the  proper  distance  from  the  inner  face  of  the 
recess  c,  the  brick  or  tile  being  laid  up  against  the  guide, 
which  is  slid  along  as  the  work  progresses.  Care  must  be 
taken  to  see  that  this  space  is  really  left  free  and  not  filled 
with  mortar  and  rubbish,  as  on  it  depends  the  operation  of 
the  joint.  All  the  space  will  ultimately  be  nearly  filled  by 
the  expansion  of  the  brick.  A  drainage,  or  “weep,”  hole, 
must  always  be  left  at  the  lowest  point,  so  that  water  cannot 
gather  in  the  expansion  space.  No  nails  should  be  used  to 
fasten  the  expansion  joint  to  anything.  Brick  are  laid 
exactly  the  same  as  the  vitrified  tile  shown  in  Fig.  5,  except 
that  the  copper  form  is  made  deeper  to  allow  for  the  greater 
thickness  of  the  brick. 


SUBSURFACE  WATERPROOFING 

42.  If  the  waterproofing  layer  is  to  be  buried  out  of 
sight  and  not  exposed  to  the  action  of  the  elements,  a  coat¬ 
ing  of  gravel  or  slag  becomes  unnecessary  and  is  therefore 
omitted.  As  has  already  been  stated,  the  essential  principle 
of  the  membrane  method  of  waterproofing  consists  in  con¬ 
structing  a  complete  and  continuous  envelope  around  the 
space  to  be  waterproofed.  It  is  of  course  preferable  to  put 
the  waterproofing  on  the  outside  of  the  foundations,  because 
the  water  will  serve  to  press  it  more  tightly  against  the  walls, 
while  if  it  is  put  on  the  inside,  the  water  pressure  will  tend  to 
lift  it  off  the  wall. 


42 


WATERPROOFING  OF  CONCRETE 


§42 


To  protect  the  waterproofing  from  blows,  abrasion,  or  wear 
from  the  outside,  either  a  thin  wall  of  concrete  or  a  single 
course  of  brick  is  usually  built  next  to  the  earth  or  adjacent 
foundations,  and  the  waterproof  layer  is  applied  to  the 
inside  of  this  wall.  The  waterproofing  is  then  sometimes 
plastered  with  an  inch  coat  of  cement  mortar  before  the 
main  foundation  walls  are  placed  against  it.  In  the  case  of 
floors  and  footings,  the  waterproofing  layer  is  carried  under¬ 
neath  and  the  foundation  floors  are  laid  directly  on  it. 

The  most  difficult  and  important  points  encountered 
in  waterproofing  are  the  work  of  carrying  the  covering 
safely  around  corners  and  the  turning  of  angles.  In  such 
places,  the  felt  should  be  cut  and  fitted  in  small  pieces  and  a 
small  hand  mop  should  be  used,  great  care  being  taken  to 
press  the  felt  into  the  hot  tar  or  asphalt  and  to  make  sure  that 
there  is  a  perfect  union  between  them. 

43.  Specifications  for  Subsurface  Waterproofing, 
Etc. — The  following,  which  are  the  Barrett  general  specifica¬ 
tions  for  using  coal-tar  pitch  to  damp-proof  or  waterproof 
courses  in  basements,  subways,  pits,  etc.,  have  proved  satis¬ 
factory.  Following  these  specifications  are  general  directions 
for  the  work  from  the  same  source. 

Thickness  of  Waterproofing  to  Resist  Water  Pressure. — The  thick¬ 
ness  of  the  damp,  or  waterproofing,  course  should  be  determined  by 
the  amount  of  dampness  and  the  head  of  water  to  be  excluded,  as 
well  as  by  the  importance  of  the  work,  and  should  vary  from  a 
minimum  of  three  plies  of  felt  and  four  moppings  of  pitch,  where  the 
dampness  of  comparatively  dry  soil  is  to  be  excluded,  up  to  a  max¬ 
imum  of  ten  plies,  where  there  is  a  considerable  head  of  water  to  con¬ 
tend  with.  A  good  rule  is  to  use  five  plies  of  felt  and  six  moppings  of 
pitch  for  any  actual  head  of  water  up  to  10  feet,  and  for  every 
additional  5  feet  of  head,  add  one  ply  of  felt  and  one  mopping  of. 
pitch. 

Purport. — It  is  the  intention  of  these  specifications  to  secure  struc¬ 
tures  against  dampness,  so  that  the  interior  shall  be  permanently  free 
from  moisture  due  to  the  percolation  of  water  from  outside  sources, 
by  means  of  a  continuous,  flexible  sheet  of  waterproofing  surrounding 
the  exterior,  bottom  and  sides,  to  a  height  safely  above  that  which  the 
water  may  reach. 


WATERPROOFING  OF  CONCRETE 


43 


Material. — The  material  shall  be  straight-run  coal-tar  pitch,  dis¬ 
tilled  direct  from  American  coal  tar,  with  a  binder  of  tarred  felt 
weighing  not  less  than  14  pounds  per  100  square  feet,  single  thick¬ 
ness.  The  pitch  when  applied  shall  be  at  a  temperature  of  not  less 
than  250°  F. 

Application. — The  surface  on  which  the  waterproofing  is  to  be 
applied  shall  be  comparatively  smooth,  and,  if  practicable,  dry.  This 
surface  shall  first  be  coated  with  a  mopping  of  hot  coal-tar  pitch,  and 
into  this  pitch,  while  it  is  still  hot,  embed  the  first  ply  of  felt,  lapping 
each  strip  of  felt  2  inches  over  the  preceding  one.  Follow  this  with 
alternating  layers  of  pitch  and  felt.  The  first  layer  of  felt  on  sides  is 
to  be  laid  from  right  to  left,  and  the  second  from  left  to  right.  The 
floor,  or  flat,  layers  are  to  be  laid  first  lengthwise  of  building  and  then 
crosswise.  Each  layer  of  pitch  laid  as  directed  must  completely  and 
entirely  cover  the  surface  on  which  it  is  spread,  without  cracks  or 
blowholes.  The  felt  in  every  case  must  be  applied  to  the  pitch  while  the 
latter  is  still  hot,  and  it  must  be  pressed  against  the  pitch  so  as  to 
insure  its  being  completely  stuck  to  the  pitch  over  the  entire  surface. 
Care  must  be  taken  that  all  joints  in  the  felt  are  well  broken  and  that 
the  ends  of  the  bottom  layers  are  carried  up  inside  the  layers  on  the 
sides,  so  as  to  insure  a  full  lap. 

None  but  competent  workmen  especially  skilled  in  this  kind  of  work 
shall  be  employed. 

Until  this  waterproofing  is  covered,  care  must  be  taken  not  to  break, 
tear,  or  injure  it  in  any  way. 

Note  1. — Protection  for  Waterproofing. — Where  earth  is  to  be  filled 
in  against  the  waterproofing,  it  shall  be  protected  by  a  4-inch  brick 
wall  or  by  a  concrete  partition. 

Note  2.- — Reservoirs. — In  case  of  reservoirs,  the  waterproofing  shall 
be  placed  on  the  inside  and  shall  be  protected  by  a  layer  of  either 
brick  or  concrete. 

Note  3. — Tunnels. — In  case  of  tunnel  work,  the  ends  of  the  layers 
shall  be  carried  down  on  to  the  side  layers  and  the  side  layers  carried 
up  on  to  the  top  layers  alternately,  so  as  to  secure  a  full  and  complete 
bond,  lapping  at  least  12  inches. 

44.  Waterproofing  Through  Foundations  and  Col¬ 
umns. — In  the  case  of  buildings,  the  wall  waterproofing 
course  should  be  carried  through  the  foundation  of  walls 
and  under  the  grillage  of  columns  on  a  line  as  near  as  prac¬ 
ticable  with  the  main  line  of  waterproofing  in  the  floor. 
Each  ply  of  felt  should  extend  at  least  20  inches  inside  the 
foundations  and  on  all  sides  of  the  column  footings.  The 

joints  in  this  waterproofing,  as  in  all  other  cases,  must  be 

211—39 


44 


WATERPROOFING  OF  CONCRETE 


§42 


broken.  These  20-inch  extensions  must  be  carefully  pro¬ 
tected  during  the  erection  of  walls  or  columns,  and  a  perfect 
bond  must  be  made  between  these  extensions  and  the  floor 
waterproofing. 

Where  the  foundation  is  on  solid  rock,  no  settlement  is  to 
be  expected;  but  where  this  is  not  the  case,  it  is  considered 
good  practice  to  substitute  sheets  of  soft  copper  for  the 
waterproofing  course  under  the  grillage  beams.  This  allows 
a  certain  amount  of  settlement  to  take  place  without  dam¬ 
age  and  is  particularly  important,  because  the  maximum  load 
does  not  come  on  the  pillars  of  a  building  until  the  struc¬ 
ture  is  practically  completed,  or  long  after  the  foundations 
and  waterproofing  are  in  place. 

45.  Pipe  Connections.— The  holes  made  in  waterproof¬ 
ing  to  admit  pipes  and  other  small  apparatus  that  pierce  the 
membranous  envelope  may  be  made  tight  by  the  use  of 
two  flanges.  These  flanges  fit  the  pipe  tightly  and  clamp 
the  waterproofing  fast  between  them. 

46.  Teaks  and  Ground  Water. — Where  leaks  are  dis¬ 
covered  in  the  completed  waterproofing,  the  membrane 
around  the  leak  must  be  cut  out,  the  trouble  traced  to  its 
source,  and  the  hole  plugged.  The  difficulty  encountered 
in  stopping  a  leak  will  emphasize  the  advantage  of  making 
a  water-tight  job  in  the  first  place. 

Where  springs  or  considerable  ground  water  are  encoun¬ 
tered,  ingenuity  must  be  exerted  to  keep  the  moisture  out 
until  the  waterproofing  is  in  place  and  well  supported. 
Sumps  are  built  below  the  floor  level  and  the  water  allowed 
to  run  into  them,  when  it  is  pumped  out.  All  the  adjacent 
portion  of  the  foundation  is  waterproofed,  and  the  sump  is 
pumped  dry,  rapidly  lined  with  pitch  and  felt,  and  the  laps 
connected  up;  then  the  hole  is  filled  with  a  mass  of  concrete 
to  resist  the  water  pressure. 

47.  Interruptions. — Owing  to  the  necessity  of  carry¬ 
ing  on  the  other  parts  of  the  work  at  the  same  time  as  the 
waterproofing,  and  to  the  need  of  storing  materials,  erecting 


WATERPROOFING  OF  CONCRETE 


45 


§  42 

derricks,  and  so  forth,  the  work  is  liable  to  constant  and  vexa¬ 
tious  interruptions.  Under  all  such  circumstances,  it  must 
constantly  be  borne  in  mind  that  the  finished  work  must  at 
all  times  be  protected  from  abrasion  or  blows  until  finally 
covered  in  by  permanent  masonry;  also,  that  where  work  is 
left  to  which  later  work  must  be  attached,  the  laps  necessary 
to  make  a  good  bond  should  invariably  be  left  and  prop¬ 
erly  protected. 

48.  Waterproofing  of  Wet  or  Damp  Surfaces. — If 

the  surface  upon  which  the  waterproofing  is  to  be  placed 
cannot  very  well  be  kept  dry,  or  if  it  is  simply  damp,  then  it 
should  be  coated  with  a  layer  of  hot  pitch,  and  after  this  has 
hardened,  a  second  layer  should  be  applied,  in  which  the  first 
ply  of  felt  is  to  be  embedded  while  the  pitch  is  still  hot. 

When  the  surface  is  actually  wet,  it  should  be  sprinkled 
with  hot  pitch  and  a  layer  of  felt  in  lengths  not  exceeding 
6  feet  should  be  placed  on  this  wet  surface  until  it  is  entirely 
covered  by  a  single  layer  of  felt.  This  surface  should  then 
be  coated  with  a  layer  of  hot  pitch  and  the  first  layer  of  felt 
embedded  in  the  pitch  while  the  latter  is  still  hot. 


INDEX 


Note. — All  items  in  this  index  refer  first  to  the  section  (see  the  Preface)  and  then  to  the 
page  of  the  section.  Thus,  “Arch  brick,  §31,  p34,”  means  that  arch  brick  will  be  found  on 
page  34  of  section  31. 


A 

Abrasion,  Resistance  of  stones  to,  §31,  p26. 
Abrasive  strength  of  cement  mortar,  §29,  p27. 
Absorptive  power  of  building  stone,  §31,  p25. 
Acid  open-hearth  process  in  making  steel, 
§40,  pll. 

Acids,  Resistance  of  stones  to,  §31,  p27. 
Adhesive  strength  of  cement  mortar,  §29,  p26. 
Adjustment  of  fire  insurance  rates,  §42,  pl6. 
Aggregate,  Definition  of,  §30,  pi;  §36,  pl7. 
on  strength  of  concrete,  Effect  of  size  of, 
§30,  p9. 

Aggregates,  Comparative  values  of,  §30,  pll. 
Desirable  properties  of,  §30,  p3. 

Selection  of,  §30,  p9. 

Size  of,  §30,  p3. 

Table  showing  the  compressive  strength  of 
concrete  made  of  different  sized,  §30,  plO. 
Air  space  in  concrete  building  block,  §36,  pll ; 
§37,  pl6. 

Alabaster,  §31,  pl2. 

Allowable  unit  stresses  for  brick  masonry, 
Table  of,  §31,  p41. 

Alloy  steel,  §40,  pl5. 

Aluminum,  Strength  of,  §40,  pl8. 

American  bond  in  brickwork,  §33,  p6. 

Anchor  for  ashlar  work,  §32,  p27. 
pile,  §39,  pi. 

Angles,  Bonding  of  walls  at,  §33,  pl2. 
Apartment  houses,  Live  loads  for,  §41,  pl3. 
Arch  brick,  §31,  p34. 

for  foundations,  Elliptic,  §32,  p53. 

Inverted,  §32,  p50. 

for  foundations,  Three-centered,  §32,  p53. 
Arenaceous  quartz,  §31,  pl3. 

Ar£nes,  Definition  of,  §29,  p9. 

Argillaceous  limestone,  §31,  plO. 

Armory,  Live  loads  for,  §41,  pl3. 

Ashlar,  Backing,  §32,  p26. 

Best  stone  for,  §32,  p26. 

Block-in-course,  §32,  p23. 


Ashlar —  (Continued) 

Broken,  §32,  p25. 

Coursed,  §32,  p22. 

Laying  out,  §32,  p26. 
masonry,  §32,  p21. 

Method  of  fastening,  §32,  p27. 

Random -coursed,  §32,  p24. 

Asphalt,  Definition  of,  §42,  p34. 

Trinidad  pitch-lake,  §42,  p34. 

Venezuelan,  §42,  p34. 

Automatic  sprinkler,  §42,  pl4. 

Ax  for  stone  cutting,  §32,  pi. 

Tooth,  §32,  p2. 

B 

Backing  ashlar,  §32,  p26. 

Ball  rooms,  Live  loads  for,  §41,  pl3. 

Band  saw  for  cutting  stone,  §32,  p4. 

Bar,  Slice,  §34,  p47. 

-twisting  machine,  §34,  p48. 

Barrett  specifications,  §42,  p36. 

Barrow,  Tray  mortar,  §34,  p37. 

Barrows  for  concrete,  §34,  p36. 

Bars,  Tools  for  bending,  §34,  p49. 

Basalt,  §31,  p7. 

Basic  open-hearth  process  in  making  steel, 
§40,  pll. 

Bat,  Definition  of,  §33,  p3. 

Half,  §33,  p4. 

Quarter,  §33,  p4. 

Three-quarter,  §33,  p4. 

Batch  mixers,  Concrete,  §34,  pll. 

Beam  grillage,  Steel-,  §38,  p5. 

support  for  lintel,  §32,  p36. 

Beams,  Table  of  depth,  weight,  and  section 
modulus  of  standard  steel,  §38,  pl8. 
used  for  grillages,  Table  of  safe  load  on 
steel,  §38,  pl5. 

Bearing  of  piles,  Engineering  News  formula 
for,  §39,  p32. 

of  piles,  Table  of  formulas  of,  §39,  p34. 


211—45 


vii 


3 


Vlll 


INDEX 


Bearing — (Continued) 

of  screw  and  disk  piles,  §39,  p34. 
pile,  §39,  pi. 

piles,  Factor  of  safety  for,  §39,  p33. 
pile,  Metal,  §39,  pl4. 
piles,  Strength  of,  §39,  p29. 
piles,  Wooden,  §39,  p2. 

Bending  rods,  Tools  for,  §34,  p49. 
strength  of  brick,  §31,  p39. 
strength  of  building  stone,  §31,  pp20,  27. 
strength  of  concrete  building  blocks, 
§36,  pl2. 

Bessemer  converter,  §40,  pl2. 

process,  §40,  pll. 

Binder,  Definition  of,  §42,  p33. 

Bituminous  cement,  §29,  pl3. 
concrete,  §30,  pi. 
material,  Definition  of,  §42,  p33. 
membranes  for  waterproofing,  §42,  p33. 
Blast  furnace,  §40,  p3. 

-furnace  slag  for  concrete,  §30,  pl4. 

Blister  steel;  §40,  pl4. 

Block,  Air  space  in  concrete  building, 
§36,  pll. 

Cement,  §36,  p2. 

Definition  of  concrete  building,  §36,  pi. 
Definition  of  hollow,  §36,  p4. 

Form  of  concrete  building,  §36,  p40. 
History  of  concrete  building,  §36,  pi. 
-in-course  ashlar,  §32,  p23. 
machine,  as  to  size,  Adjustability  of, 
§36,  p40. 

machine,  Ease  of  condensation  in,  §36,  p42. 
machine,  Ease  of  discharge  from,  §36,  p43. 
machine,  Facility  of  filling,  §36,  p41. 
machine,  Ideal,  §36,  p29. 
machine,  Miracle,  §36,  p29. 
machine,  Provision  for  facing  in,  §36,  p43. 
machine,  Rapidity  of  operation  of,  §36,  p43. 
machine,  Variation  in  shape  allowed  in, 
§36,  p41. 

machines,  Compressing  concrete  in,  §36,  p34. 
Machine,  Selection  of,  §36,  p39. 
machines,  to  use  of  wet  material,  Adapt¬ 
ability  of,  §36,  p42. 

One-piece  concrete  building,  §36,  p4. 
plant,  Arrangement  of  machinery  for  con¬ 
crete,  §36,  p44. 

plant,  Selection  of  workmen  for,  §36,  p46. 
Size  and  weight  of  concrete  building,  §36,  p8. 
Two-piece  concrete  building,  §36,  p6. 

Use  and  efficiency  of  building,  §36,  p3. 
Blocked -course  ashlar,  §32,  p23. 

Blocks,  Appearance  of  concrete  building, 
§36,  pl5. 

Arrangement  and  equipment  of  factory  for 
concrete  building,  §36,  p39. 


Blocks — (Continued) 

by  machinery,  Mixing  building,  §36,  p26. 
Composition  of  concrete  building,  §36,  pi 7. 
Compressing  and  pouring  concrete,  §36,  p34. 
Condensation  and  curing  of  concrete  build¬ 
ing,  §36,  plS. 

Density,  impermeability,  and  durability  of 
concrete  building,  §36,  pl3. 

Depositing  concrete  for  building,  §36,  p27. 
Essential  qualities  of  building,  §36,  pi 2. 
Facing  concrete  building,  §36,  p32. 

Factors  affecting  the  qualities  of  concrete 
building,  §36,  pl7. 

Fire  resistance  of  concrete  building,  §36,  pl4. 
Inspection  of  materials  for  concrete  build¬ 
ing,  §36,  p21. 

Manufacturing  process  of  building,  §36,  p21 . 
Materials  of  manufacture  for  concrete, 
§36,  pl8. 

Mixing  by  hand  concrete  building,  §36,  p25. 
Mixing  concrete  building,  §36,  pl7. 
Moisture  used  in  building,  §36,  pi 7. 
Off-bearing  and  curing  building,  §36,  p36. 
Proportioning  materials  for  building, 
§36,  p23. 

Shape  of  concrete,  §36,  p4. 

Strength  of  concrete  building,  §36,  pi 2. 
Blowing,  Definition  of,  §29,  p4. 

Bluestone,  §31,  p9. 

Board,  Stock,  §31,  p30. 

Boilers,  Instructions  for  starting  and  man¬ 
aging,  §34,  p33. 

Boiling  test  of  cement,  §35,  pl2;  §34,  p8. 
Bolting,  Drift,  §39,  pll. 

Bond,  American,  §33,  p6. 

Diagonal,  §33,  p8. 

Double  Flemish,  §33,  p6. 

English,  §33,  p5. 

Flemish,  §33,  p5. 

Garden,  §33,  p6. 

Heading,  §33,  p4. 

Herring-bone,  §33,  p8. 
in  brickwork,  §33,  p4. 
of  concrete,  Allowable,  §30,  p25. 
of  concrete  building  block,  §37,  p3. 
Running,  §33,  p6. 
stones,  §32,  p31. 

Stretching,  §33,  po. 

Bonding  brick  walls,  §33,  pi. 

Necessity  of  preserving,  §33,  p2. 
of  face  brick,  §33,  p8. 
of  hollow  walls,  §33,  plO. 
of  walls  at  angles,  §33,  pl2. 
thin  ashlar,  §32,  p27. 

Toothed,  §32,  p27. 
with  metal  ties,  §33,  p9. 

Boom  derrick,  §34,  p39. 


INDEX 


IX 


Bottom,  Definition  of,  §31,  p30. 

Boulders  for  concrete,  Broken,  §30,  pl3 
Brard’s  test  of  freezing,  §31,  p26. 

Brass,  Composition  of,  §40,  pl7. 

Strength  of,  §40,  pl8. 

Brecciated  marbles,  §31,  pl2. 

Brick,  Arch,  §31,  p34. 

Bonding  of  face,  §33,  p8. 
burning,  §31,  p33. 

Circle,  §31,  p34. 

Classification  of  clay,  §31,  p34. 

Clinker,  §31,  p34. 

Common,  §31,  p34. 

Composition  of,  §31,  p29. 

Dressed,  §31,  p33. 

Enameled,  §31,  p35. 

Face,  §31,  pp33,  34. 

Gauged,  §31,  p34. 

Glazed,  §31,  p35. 

Hand-made,  §31,  p30. 

Hard,  §31,  p34. 

in  severe  weather,  Laying,  §33,  pl4. 
Machine-made,  §31,  p31. 

Manufacture  of  clay,  §31,  p30. 
Manufacture  of  sand-lime,  §31,  p38. 
masonry,  Table  of  allowable  unit  stresses 
for,  §31,  p41. 

Molded,  §31,  pp33,  34. 

Pale,  §31,  p33. 

Paving,  §31,  p36. 

Pressed,  §31,  pp33,  34. 
quoins,  Walls  with,  §32,  p20. 

Red,  §31,  p34. 

Roof  covered  with  tile  or,  §42,  p42. 
roofs,  Expansion  joints  for  vitrified-tile  or, 
§42,  p40. 

Salmon,  §31,  pp33,  34. 
sidewalks,  §32,  p57. 

Size  of,  §31,  p39;  §33,  pl5. 

Soft,  §31,  p34. 

Stock,  §31,  p34. 

Strength  of,  §31,  p39. 
wall,  Curtain,  §33,  p29. 
wall,  Enclosure,  §33,  p29. 
wall,  Hollow,  §33,  p28. 
wall,  Party,  §33  p28. 
walls,  Bonding,  §33,  pi. 
walls  for  dwelling  houses,  Table  of  thick¬ 
ness  of,  §33,  p27. 

walls  for  warehouses,  Table  of  thickness  of, 
§33,  p22. 

walls,  Laws  governing  thickness  of,  §33,  pl6. 

walls,  Solid,  §33,  p28. 

walls,  Thickness  of,  §33,  pl5. 

Well-burned,  §31,  p34. 

Bricklaying,  Difficulties  in,  §33,  pl4. 
Brickwork,  Bond  in,  §33,  p4. 


Brickwork — (Continued) 

Table  of  strength  of,  §31,  p41. 

Weight  of,  §31,  p41. 

Briquet  clip,  Form  of,  §35,  p22. 

Definition  of,  §35,  pl4. 

Form  of,  §35,  pl7. 

Molds  for,  §35,  pl7. 

Table  of  tensile  strength  of  cement,  §35,  p23. 
Briquets,  Method  of  making,  §35,  pl8. 

Storage  of,  §35,  pl9. 

Broached  work,  §32,  pp4,  6. 

Broken  ashlar,  §32,  p25. 

boulders  for  concrete,  §30,  pl3. 
granite  for  concrete,  §30,  pl3. 
limestone  for  concrete,  §30,  pl4. 
slate  for  concrete,  §30,  pi 5. 
stone,  Comparative  values  of,  §30,  pll. 
stone,  Desirable  properties  of,  §30,  p3. 
stone  for  concrete  building  blocks,  §36,  pl9. 
stone  on  strength  of  concrete,  Effect  of  size 
of,  §30,  p9. 

stone,  Size  of,  §30,  p3.  v 

stone  used  in  concrete,  Table  of  com¬ 
parative  value  of  different,  §30,  pl2. 
Bronze,  Composition  of,  §40,  p20. 

Strength  of,  §40,  pl8. 

Brown  hematite,  Composition  of,  §40,  p2 
Brownstone,  §31,  p8. 

Brush  finish  for  concrete,  §34,  p53. 

Bucket  hoist,  §34,  p41. 

Hoisting,  §34,  p41. 

Building  block,  Air  space  in  concrete,  §36,  pll. 
block,  Cost  of  concrete,  §37,  plO. 
block,  Definition  of  concrete,  §36,  pi. 
block,  Form  of  concrete,  §36,  p40. 
block,  History  of  concrete,  §36,  pi. 

-block  industry,  Failure  in,  §37,  p9. 

-block  machine,  Condensation  in,  §36,  p42. 
-block  machine,  Facility  of  filling,  §36,  p41. 
-block  machine,  Perfection  of  discharge 
from  concrete,  §36,  p43. 

-block  machine,  Provision  for  facing  in, 
§36,  p43. 

-block  machine,  Rapidity  of  operation  of, 
§36,  p43. 

-block  machine,  to  size,  Adjustability  of, 
§36,  p40. 

-block  machine.  Variation  of  shape  of  block 
allowed  in,  §36,  p41. 

-block  machines,  Selection  of,  §36,  p39. 
-block  machines,  to  use  of  wet  material, 
Adaptability  of,  §36,  p42. 

-block  manufacturer,  Certificate  for, 
§37,  pl7. 

block,  One-piece  concrete,  §36,  p4. 

-block  partitions,  Concrete,  §37,  p6. 

-block  plant,  Machinery  for,  §36,  p44. 


X 


INDEX 


Building — (Continued) 

block  plant.  Selection  of  workmen,  §36,  p46. 
block,  Shape  of  concrete,  §36,  p4. 
block,  Size  and  weight  of  concrete,  §36,  p8. 
block,  Two-piece  concrete,  §36,  p6. 
block,  Use  and  efficiency  of  concrete,  §36,  p3. 
-block  wall,  Pilaster  in  concrete,  §37,  p5. 
blocks,  Air  spaces  for,  §37,  pl6. 
blocks,  Appearance  of  concrete,  §36,  pl5. 
blocks,  Arrangement  and  equipment  of  fac¬ 
tory  for  concrete,  §36,  p39. 
blocks,  Bond  of  concrete,  §37,  p3. 
blocks,  Cement,  gravel,  and  sand  for, 
§37,  pl3. 

blocks,  Coloring  matter  for  concrete, 
§37,  pl4. 

blocks,  Composition  of,  §36,  pi 7. 
blocks,  Composition  of  mortar  for,  §37,  p3. 
blocks,  Condensation  and  curing  of,  §36,  pl8. 
blocks,  Condensation  of,  §37,  pl5. 
blocks,  Consistency  of  concrete  for,  §37,  pl4. 
blocks,  Curing  concrete,  §37,  pl6. 
blocks,  Density,  impermeability,  and  dura¬ 
bility  of  concrete,  §36,  pl3. 
blocks,  Depositing  concrete  for,  §36,  p27. 
blocks,  Details  of  making  and  laying  con¬ 
crete,  §37,  pi. 

blocks,  Essential  qualities  of,  §36,  pl2. 
blocks,  Facing  concrete,  §36,  p32;  §37,  pl5 
blocks.  Factors  affecting  the  qualities  of 
concrete,  §36,  pi 7. 

blocks,  Fastening  plates  to  concrete,  §37,  p5. 
blocks,  Fire  resistance  of  concrete,  §36,  pl4. 
blocks.  Fitting  concrete,  §37,  pp2,  3. 
blocks,  Footings  and  foundations  for  con¬ 
crete,  §37,  pi. 

blocks  for  chimney  flues,  §37,  p7. 
blocks  for  comers,  §37,  p7. 
blocks  for  jambs,  Concrete,  §37,  p6. 
blocks  for  sills,  lintels,  and  ornamental 
members,  Concrete,  §37,  p8. 
blocks  for  special  uses.  Concrete,  §37,  p6. 
blocks,  Inspection  of  materials  for  con¬ 
crete,  §36,  p21. 

blocks,  Laying  concrete,  §37,  pl6. 
blocks,  Manufacturing  process  of,  §36,  p21. 
blocks,  Materials  of  manufacture  for  con¬ 
crete,  §36,  pl8. 

blocks,  Mixing,  by  hand,  §36,  p25. 
blocks,  Mixing,  by  machinery,  §36,  p26. 
blocks,  Mixing  concrete,  §36,  pl7;  §37,  pl4. 
blocks,  Moisture  used  in  concrete,  §36,  pl7. 
blocks,  Mortar  joints  for  concrete,  §37,  p2. 
blocks,  Nailing  to  concrete,  §37,  p6. 
blocks,  Off-bearing  and  curing,  §36,  p36. 
blocks,  Proportion  of  ingredients  for, 
§37,  pl4. 


B  uilding — (Continued) 

blocks,  Proportioning  materials  for  con¬ 
crete,  §36,  p22. 

blocks,  Specifications  of  concrete,  §37,  pl3. 
blocks,  Strength  of  concrete,  §36,  pl2. 
blocks,  Supporting  floor  joists  on,  §37,  p4. 
blocks,  Tamping,  compressing,  and  pouring 
concrete,  §36,  p34. 
blocks,  Testing  concrete,  §37,  pl6. 
blocks,  Wall  construction  of  concrete 
§37,  p4. 

blocks,  Width  of  walls  of  concrete,  §37, 
pp4,  16. 

law  regulations  for  stress  in  concrete, 
Table  of,  §30,  p26. 
material,  Handling  of,  §34,  pp5,  8. 
materials,  Table  of  weight  of,  §41,  p2. 
Buildings,  Inspection  of  stone  in,  §31,  p23. 
Built-up  lintel,  §32,  p37. 

Burning  brick,  §31,  p33. 

Bush  hammer,  §32,  p3;  §34,  p54. 

-hammered  work,  §32,  pll. 

C 

Calcination,  Definition  of,  §29,  pi. 

Calcium  stearate,  §42,  p28. 

Cantilever  foundations,  §38,  p44. 

foundations,  Construction  details  of, 
§38,  p44. 

foundations,  Design  of,  §38,  p50. 

Cap,  Definition  of,  §32,  p34. 

Capping  concrete  piles,  §39,  p38 
Granite,  §39,  pl2. 

Grillage,  §39,  pll. 
of  wooden  piles,  §39,  pll. 

Carbon,  Combined,  §40,  p6. 

Graphitic,  §40,  p6. 
in  cast  iron,  §40,  p6. 

Care  and  inspection  of  reinforcement,  §34,  p8. 
of  building  materials,  §34,  pp5,  8. 
of  lumber  for  form  work,  §34,  plO. 

Carlin  cube  mixer,  §34,  pl3. 

Carts  for  concrete,  §34,  p34. 

Cast  iron,  Carbon  in,  §40,  p6. 
iron,  Characteristics  of,  §40,  p6. 
iron,  Production  of,  §40,  p5. 
iron,  Silicon,  sulphur,  phosphorus,  and 
manganese  in,  §40,  p6. 
iron,  Strength  of,  §40,  pl8. 

Casting,  Definition  of,  §40,  pi. 

Cement,  Accelerated  tests  of,  §35,  pll. 
Adaptability  of,  §29,  pi 2. 

Bituminous,  §29,  pl3. 
block,  §36,  p2. 

Boiling  test  of,  §35,  pi 2. 

briquet,  Form  of,  §35,  pl7. 

briquets,  Table  of  strength  of,  §35,  p23. 


INDEX 


xi 


Cement — (Continued) 

Causes  of  unsoundness  of,  §35,  p6. 
Chemical  analysis  of,  §35,  pp4,  34. 
Coal-tar,  §29,  pl3. 

coatings,  Waterproofing  with,  §42,  p31. 
Color  of,  §29,  pll. 

Composition  of,  §29,  plO. 

Constancy  of  volume  of,  §35,  p5. 

Containers  for,  §34,  p6. 

Definition  of,  §29,  pi. 

Definition  of  mixed,  §29,  p7. 

Definition  of  natural,  §29,  p6. 

Definition  of  puzzolan,  §29,  p7. 

Description  of,  §36,  pl8. 

Determination  of  soundness  of,  §35,  p6. 
Distinguishing  characteristics  of,  §29,  pl2. 
Field  inspection  of,  §35,  pi. 
for  building  blocks,  §37,  pl3. 
grout,  §29,  p30. 

Improved,  §29,  p7. 

Keene’s,  §29,  pl3. 

Lafarge,  §32,  p29. 

Louisville,  §29,  p8. 

Manufacture  of  improved,  §29,  p9. 
Manufacture  of  natural,  §29,  p8. 
Manufacture  of  Portland,  §29,  p7. 
Manufacture  of  puzzolan,  §29,  p8. 
Measurement  of  expansion  of,  §35,  p6. 
mortar,  §29,  p20;  §30,  p2. 
mortar,  Abrasive  strength  of,  §29,  p27. 
mortar,  Adhesive  strength  of,  §29,  p26. 
mortar,  Compressive  strength  of,  §29,  p26. 
mortar  in  freezing  weather,  Laying,  §29,  p28. 
mortar,  Ingredients  of,  §29,  p20. 
mortar,  Mixing,  §29,  p23. 
mortar,  Retempering,  §29,  p27. 
mortar,  Shrinkage  of,  §29,  p29. 
mortar,  Strength  of,  §29,  p25. 
mortar,  Table  of  materials  required  per 
cubic  yard  of,  §29,  p23. 
mortar,  Tensile  strength  of,  §29,  p26. 
mortars,  Coloring  of,  §29,  p31. 
mortars,  Properties  of,  §29,  p25. 
mortars,  Proportion  of  ingredients  of 
various,  §29,  p21. 

mortars,  Table  of  ultimate  tensile  strength 
of,  §29,  p25. 

mortars,  Waterproofing  of,  §29,  p30. 
Natural,  §36,  pl8. 

Neat,  §30,  pi. 

Non-staining,  §29,  pl3. 

Normal  consistency  of,  §35,  pl4. 

Normal  test  of,  §35,  p7. 

packages.  Weight  and  condition  of,  §35,  pi. 

Parian,  §29,  pl3. 

Physical  properties  of,  §29,  pll. 

Portland,  §36  pl8. 


Cement — (Continued) 

Portland,  Definition  of,  §29,  p6. 

Properties  of,  §29,  plO. 

Purpose  of  testing,  §35,  p4. 

Puzzolan,  §36,  pl8. 

Results  of  tests  of  soundness  of,  §5,  pl3. 
Roman,  §29,  p8. 

Rosendale,  §29,  p8. 

Sampling  of,  §35,  p3. 

Sand,  §29,  p9. 

sand,  Definition  of,  §29,  p7. 

seasoning,  §35,  p6. 

Second-grade  Portland,  §29,  pi. 

Selection  of,  §36,  p22. 
sidewalks,  §32,  p57. 

Silica,  §29,  p9. 

Slag,  §29,  p9. 

Soundness  of,  §35,  pp4,  5. 

Specifications  for  Portland,  §35,  p36. 
Steam  test  of,  §35,  pi 3. 

Storing  of,  §34,  p5. 

Tensile  strength  test  of,  §35,  pp4,  14. 
testing,  Difficulties  of,  §35,  p5. 

-testing  machine,  §35,  p20. 

-testing  machine,  Beam  type,  §35,  p21. 
-testing  machine,  Shot,  §35,  p20. 

Testing  of,  §34,  p7. 

tests,  Classification  of,  §35,  p4. 

Tests  of  natural  and  slag,  §35,  p36. 
tests,  Primary,  §35,  pp4,  5. 
tests,  Secondary,  §35,  p4,  24. 

Weight  of,  §29,  pll. 

White  Portland,  §36,  pl9. 

Cementing  materials,  Miscellaneous,  §29,  pl2. 

materials,  Uses  of,  §29,  pi. 

Cements,  Classification  of,  §29,  p6. 

Classification  of  limes  and  hydraulic,  §29,  p2. 
Manufacture  of  mixed,  §29,  p9. 

Table  of  requirements  for  high-grade, 
§35,  p27. 

Center  of  gravity  of  rectangular  compound 
footing,  Location  of,  §38,  p20. 

Centering,  Construction  of,  §34,  p51. 
Definition  of,  §30,  p29. 

Filling  the,  §34,  p52. 

Precautions  for,  §34,  p51. 

Stripping  the,  §34,  p52. 

Certificate  for  concrete  building -block  manu¬ 
facturer,  §37,  pi 7. 

Chalk,  §31,  pl2. 

Charging  hoppers,  §34,  p37. 

Chatelier  flask,  Le,  §35,  p33. 

Checkerwork,  Definition  of,  §40,  p4. 

Chelura,  §39,  p2. 

Chemical  analysis  of  building  stone,  §31,  p24. 

analysis  of  cement,  §35,  pp4,  34. 
Chenoweth  steel-concrete  pile,  §39,  p56. 


Xll 


INDEX 


Chimney  flues,  Concrete  blocks  for,  §37,  p7. 
Chisel,  Drove,  §32,  p4. 

Pitching,  §32,  p4. 

Tooth,  §32,  p4. 

Chisels  for  stone  cutting,  §32,  p4. 

Churches,  Live  loads  for,  §41,  pl3. 

Cinder  concrete,  Definition  of,  §30,  p2. 
Cinders  for  concrete,  §30,  pl5. 

Circle  brick,  §31,  p34. 

Circular  saw  for  stone,  §32,  p4. 

Clay  brick,  Classification  of,  §31,  p34. 
brick,  Manufacture  of,  §31,  p30. 
Waterproofing  concrete  with  lime  or, 
§42,  p26. 

Cleaning  stone  masonry,  §32,  p29. 

Cleavage,  Planes  of  slaty,  §31,  p9. 

Climate  and  environment  on  building  stone, 
Effect  of,  §31,  pl5. 

Clinker  brick,  §31,  p34. 

Clip,  Form  of  briquet,  §35,  p22. 

Close  pile,  §39,  p2. 

Closer,  Definition  of,  §33,  p3. 

King,  §33,  p4. 

Queen,  §33,  p4. 

Coal  tar,  §42,  p34. 

-tar  cement,  §29,  pl3. 

-tar  pitch  and  felt  over  concrete,  Specifica¬ 
tions  for,  §42,  p36. 

Cobblestones  for  concrete,  §30,  pl3. 

Cockbum  concrete  mixer,  §34,  p21. 

Coefficient  of  elasticity  of  metals,  §40,  pl8. 

of  expansion  of  concrete,  §30,  p22. 

Colloidal  clay,  §42,  p28. 

Columns,  Footings  for  three  or  more,  §38,  p29. 

Footings  for  two.  §38,  p22. 

Combined  carbon,  §40,  p6. 

Combustion  chamber,  §40,  p4. 

Common  brick,  §31,  p34. 

lime,  §29,  p2. 

Composite  pile,  §39,  p51. 

Compound  footing,  Location  of  center  of 
gravity  of  rectangular,  §38,  p20. 
footings,  §38,  p20. 

Compression  of  concrete  building  blocks, 
§36,  p35;  §37,  plo. 

Compressive  strength  of  brick,  §31,  p39. 
strength  of  brickwork,  Table  of,  §31,  p41. 
strength  of  building  stone,  §31,  p20. 
strength  of  cement  mortar,  §29,  p26. 
strength  of  concrete  building  blocks,  §36,  pi  2. 
strength  of  concrete  made  of  different-sized 
aggregates,  Table  of,  §30,  plO. 
strength  of  concrete,  Ultimate,  §30,  p26. 
strength  of  metals,  §40,  pl8. 
stress  on  concrete,  Allowable,  §30,  p24. 
Compressol  system  of  concrete-pier  construc¬ 
tion,  §39,  p57. 


Concrete  batch  mixers,  §34,  pll. 

Bituminous,  §30,  pi. 

Broken  boulders  for,  §30,  pl3. 

Broken  limestone  for,  §30,  pl4. 

Brush  finish  for,  §34,  p53. 

bucket  hoist,  §34,  p41. 

building  blocks,  Appearance  of,  §36,  pl5. 

by  voids,  Proportioning,  §30,  pl7. 

by  weight,  Proportioning,  §30,  pl8. 

carts,  §34,  p34. 

cinder,  Definition  of,  §30,  p2. 

Cinders  for,  §30,  plo. 

Cobblestones  for,  §30,  pl3. 

Comparative  values  of  different  aggregates 
for,  §30,  pll. 

Corrosion  of  steel  in,  §30,  p20. 

Crushed  granite  used  for,  §30,  pl3. 
Customary  proportions  of,  §30,  pl8. 
Definition  of,  §30,  pi. 

Desirable  properties  of  stone  for,  §30,  p3. 
Dry,  §30,  pl9;  §37,  pl4. 

Effect  of  fire  on,  §30,  p21. 

Effect  of  vibration  on,  §30,  p23. 

Elevator  for,  §34,  p39. 

Finish  of,  §34,  p53. 

for  blocks,  Consistency  of,  §37,  pi 4. 

for  blocks,  Depositing,  §36,  p27. 

Fuller’s  rule  of  quantities  for,  §30,  p31. 
Gravel  for,  §30,  pl3. 
hoisting  bucket  §34,  p41. 
hoppers,  Charging,  §34,  p37. 
in  various  cities,  Table  of  allowable  stress 
on,  §30,  p26. 

Lime,  §30,  pi. 

Linear  coefficient  of  expansion  of,  §30,  p22. 
Materials  used  in,  §30,  pi. 

Measuring  ingredients  for,  §30,  p31. 

Medium,  §37,  pl4. 

mixer,  Carlin,  §34,  pl3. 

mixer,  Cockburn,  §34,  p21. 

mixer,  Drake,  §34,  p20. 

mixer,  Gilbreth  rotary,  §34,  pl6. 

mixer,  Gravity,  §34,  p22. 

mixer,  International,  §34,  pi 7. 

mixer,  Ransome.  §34,  pl4. 

mixer,  Selection  of,  §34,  plO;  §36,  p44. 

mixer,  Smith,  §34,  pl6. 

mixer,  Starting  and  operating  a,  §34,  p34. 

mixers,  §34,  plO. 

mixers,  Continuous,  §34,  ppll,  19. 
mixers,  Cube,  §34,  pll. 
mixers,  Hand-cart,  §34,  p29. 
mixers,  Operation  of,  §34,  p31. 
mixers,  Power  equipment  for,  §34,  p27. 
mixers,  Quantitative,  §34,  ppll,  24. 
mixing  devices,  Combined  hoisting,  §34,  p43. 
Mixing  of,  §30,  p33. 


INDEX 


xm 


Concrete — (Continued) 

mixture,  Consistency  of,  §30,  p29. 
obtained  by  proportioning  ingredients, 
Strength  and  imperviousness  of,  §30,  pl5. 
Pebbles  for,  §30,  pi 3. 

Permeability  of,  §30,  p23. 

Proportion  of  ingredients  in,  §30,  pplo,  30. 
Properties  of,  §30,  p20. 

Retempering,  §30,  p36. 
rollers,  §34,  p47. 

Selection  of  method  of  hoisting,  §34,  p39. 
Shale  for,  §30,  pl4. 

Shrinkage  of,  §30,  p21. 

Size  of  stone  for,  §30,  pp3,  9. 

Slag  for,  §30,  pi  4. 

Slate  for,  §30,  pl5. 

Spade  for  placing,  §34,  p47. 

Table  of  comparative  value  of  different 
aggregates  used  in,  §30,  pi 2. 

Table  of  quantities  of  ingredients  for, 
§30,  P34. 

Table  of  ultimate  strength  of,  §30,  p28. 
Thermal  changes  in,  §30,  p22. 

Tools  used  in  placing,  §34,  p47. 

Trap  rock  for,  §30,  pl3. 

Ultimate  strength  of,  §30,  p26. 

Water  used  in  mixing,  §30,  pl8. 

Weight  of,  §30,  p20. 

Wet,  §37,  pl5. 

with  new,  Joining  of  old,  §30,  p39. 

Working  stresses  of,  §30,  p24. 

Concreting  at  high  temperature,  §30,  p37. 

in  freezing  weather,  §30,  p37. 
Concretionary,  Definition  of,  §31,  p3. 
Condensation  of  concrete  building  blocks, 
§36,  ppl8,  42;  §37,  pl5. 

Conflagration  breeders,  §42,  p9. 
Conflagrations,  Causes  of,  §42,  p9. 

Consistency  of  cement,  Normal,  §35,  pl4. 
of  concrete  for  building  blocks,  §37,  pl4. 
of  sand  mortars,  §35,  pi 5. 
of  the  concrete  mixture,  §30,  p29. 
Constancy  of  volume  of  cement,  §35,  p5. 
Continuous  concrete  mixers,  §34,  ppll,  19. 

mixer,  Principles  of  the,  §34,  pl9. 
Converter,  Bessemer,  §40,  pl2. 

Conveying  concrete,  §34,  p34. 

Coping,  Gable,  §32,  p40. 

Kneeler,  §32,  p40. 

Stone,  §32,  p39. 

Copper,  Manufacture  of,  §40,  pl7. 

Strength  of,  §40,  pl8. 

Corrosion  of  steel  in  concrete,  §30,  p20. 
Corrugated  concrete  pile,  §39,  p53. 

concrete  pile  driving,  §39,  p54. 

Cost  of  concrete  building  block,  §37,  plO. 
of  concrete  piles,  §39,  pp59,  60. 


Cost — (Continued) 

of  concrete  piles  compared  with  wood, 
§39.  p59. 

of  fire  insurance,  §42,  pl6. 
of  waterproofing,  Approximate,  §42,  p55. 
Course,  Definition  of,  §33,  p2. 

Coursed  ashlar,  §32,  p22. 

rubble,  §32,  p20. 

Cracks,  Hair,  §32,  p58. 

Crandall  for  stone  cutting,  §32,  p3. 

Crandalled  work,  §32,  pll. 

Crucible  process,  §40,  pl2. 

Crusher  run,  §37,  pl3. 

Crushing  strength  of  brick,  §31,  p39. 

strength  of  building  stone,  §31,  p27. 
Crystalline  rock,  Example  of,  §31,  p2. 

limestone,  §31,  plO. 

Cube  concrete  mixers,  §34,  pll. 

mixer,  Carlin,  §34,. pl3. 

Cupola,  Foundry,  §40,  p5. 

Curing  concrete  building  blocks,  §36,  ppl8,  36; 
§37,  pl6. 

Steam,  §37,  pl6. 

Water,  §37,  pl6. 

Curtain  wall,  Brick,  §33,  p29. 

Cutting  and  finishing  stone,  §32,  pi. 

14 

Damp  surfaces,  Waterproofing  of  wet  and, 
§42,  p45. 

Dead  load,  §41,  pi. 

load  of  roof  trusses,  §41,  p9. 

Dense  terra  cotta,  §31,  p37. 

Density  of  building  stone,  §31,  pi. 

of  concrete  building  blocks,  §36,  pl3. 
Diagonal  bond,  §33,  p8. 

Disk  pile,  §39,  pl4. 

piles,  Bearing  of  screw  and,  §39,  p34. 
Dolomite,  §31,  plO. 

Double  best  iron,  §40,  p9. 

-faced  hammer,  §32,  pi. 

Flemish  bond,  §33,  p6. 

-sheer  steel,  §40,  pi 5. 

Draft  line,  §32,  p6. 

Drafts,  Definition  of,  §32,  pi. 

Drag  saw,  §32,  p4. 

Drake  mixer,  §34,  p20. 

Drawings,  Examination  and  care  of,  §34,  p2. 
Dressed  brick,  §31,  p33. 

Dressing  stone,  Faults  in,  §32,  p30 
Drift  bolting,  §39,  pi. 

Drips  and  washes,  §32,  p34. 

Driver,  Comparison  of  drop-  and  steam-ham¬ 
mer  pile,  §39,  p27. 

Drop-hammer  pile,  §39,  p24. 

Location  of  pile,  §39,  p28. 

Pile  §39,  p24. 


XIV 


INDEX 


Dri  ver —  (Continued) 

Steam-hammer  pile,  §39,  p26. 

Driving  inclined  pile,  §39,  p28. 
piles,  Method  of,  §39,  p23. 

Raymond  concrete  pile  by  hammer, 
§39,  p42. 

Raymond  concrete  pile  by  water  jet, 
§39,  p44. 

Drop-  and  steam-hammer  pile  driver,  Com¬ 
parison  of,  §39,  p27. 

Drove  chisel,  §32,  p4. 

work,  §32,  pll. 

Dry-clay  process,  §31,  p32. 
concrete,  §37,  pl4;  §30,  pl9. 

-mixed  concrete,  §30,  p29. 
molding,  §31,  p30. 
pan,  §31,  p32. 

Drying,  Protection  of  concrete  from  rapid, 
§34,  p53. 

Duchemin’s  formula,  §41,  p30. 

Durability  of  building  stone,  §31,  pi 4. 
of  cement,  Strength  and,  §35,  p4. 
of  concrete  building  blocks,  §36,  pl3. 
Duties  of  the  superintendent,  §34,  pi. 
Dwelling  houses,  Table  of  thickness  of  brick 
walls  for,  §33,  p27. 

houses,  Thickness  of  walls  for,  §33,  pl6. 
Live  loads  for,  §41,  pl3. 

E 

Elastic  limit  of  metals,  §40,  pl8. 

Elaterite  waterproofing  compound,  §42,  p30. 
Elevating  concrete,  §34,  p37. 

Elliptic  arch  for  foundations,  §32,  p53. 
Eminently  hydraulic  lime,  §29,  p3. 

Enameled  brick,  §31,  p35. 

Enclosure  wall,  Brick,  §33,  p29. 

Engineering  News  formula  for  bearing  of 
piles,  §39,  p32. 

English  bond,  §33,  p5. 

Expansion  joints  of  vitrified -tile  or  brick  roof, 
§42,  p40. 

of  cement,  Measurement  of,  §35,  p6. 
of  concrete,  Coefficient  of,  §30,  p22. 

Eyes,  Definition  of,  §31,  p33. 

F 

Face  brick,  §31,  pp33,  34. 
brick,  Bonding  of,  §33,  p8. 

-down  mold,  §36,  pp27,  29. 
hammer,  §32,  pi. 
plates,  Design  of,  §36,  p41 
section,  §36,  p4. 

-up  mold,  §36,  p27. 

Facing  concrete  building  blocks,  §36,  p32. 
in  concrete  building-block  machine,  Pro¬ 
vision  for,  §36,  p43. 


Facing —  (Continued) 

Mixing  of  fine,  §36,  p27. 
of  ashlar,  Method  of  fastening,  §32,  p27. 
of  concrete  building  blocks,  §37,  pl5. 
Factor  of  safety  for  piles,  §39,  p33. 

of  safety  used  in  masonry,  §31,  p21. 
Factories,  Live  loads  for,  §41,  pl3. 

Factory  for  concrete  building  blocks,  Arrange¬ 
ment  and  equipment  of,  §36,  p39. 
Failures  in  the  concrete  building-block  in¬ 
dustry,  Causes  of,  §37,  p9. 

Fan-shaped  footings,  §38,  p35. 

-shaped  footings,  Design  of,  §38,  p39. 
Farm  products,  Table  of  weight  of,  §41,  p20. 
Fat  lime,  §29,  p2. 

Feebly  hydraulic  lime,  §29,  p3. 

Feeder,  Gilbreth  measurer  and,  §34,  p25. 

Felt,  Saturated,  §42,  p40. 

Ferrous  carbonate,  Composition  of,  §40,  p2. 
Ferruginous  limestone,  §31,  plO. 

Field  inspection  of  cement,  §35,  pi. 

-stone  walls,  §32,  pl9. 

Filling  pile,  §39,  p2. 

Fine-pointed  work,  §32,  p6. 

Fineness  of  sand,  §29,  pl6. 
test,  Apparatus  for,  §35,  p28. 
test.  Method  of  making,  §35,  p29. 
test,  Reasons  for,  §35,  pp4,  27. 
tests,  Results  of,  §35,  p31. 

Finish  for  concrete,  Brush,  §34,  p53. 
for  concrete,  Hand,  §34,  p54. 
of  concrete,  §34,  p53. 
of  stonework,  §32,  p5. 

Sand-blast,  §34,  p55. 

Finishing  and  cutting  stone,  §32,  pi. 

on  building  stone,  Effect  of  quarrying  and, 
§31,  pl7. 

with  pneumatic  hammer,  §34,  p55. 

Fire,  Causes  of,  §42,  p4. 

insurance,  Cost  of,  §42,  pl6. 
insurance.  Limits  of,  §42,  pl8. 
insurance,  Purpose  of,  §42,  pi. 

-insurance  rates,  Adjustment  of,  §42,  pl6. 
on  building  stone,  Effect  of,  §31,  pl8. 
on  concrete,  Effect  of,  §30,  p21. 
protection,  Private,  §42,  pl4. 
protection,  Public,  §42,  pl5. 
record  of  various  cities,  Table  of,  §42,  p3. 
Resistance  of  building  stone  to,  §31,  p29. 
resistance  of  concrete  building  blocks, 
§36,  pl4. 

Special  causes  of,  §42,  p5. 

Firebrick,  §31,  ppl3,  35. 

Fireproof  construction,  §42,  plO. 

construction,  Object  and  requirements  of, 
§42,  pl3. 

construction,  Reinforced -concrete,  §42,  pl3. 


INDEX 


xv 


Fi  re  proof —  (Conti  nued) 

construction,  Types  of,  §42,  plO. 
floors,  Weight  of,  §41,  pi. 
skeleton  steel-frame  construction,  §42,  pl2. 
Fires,  Cause  and  prevention  of,  §24.  p2. 
Causes  of  spreading  of,  §42,  p8. 
Extinguishment  of,  §42,  pl4. 

Frequency  of,  §42,  p2. 

Prevention  of,  §42,  p6. 

Spreading  of,  §42,  p7. 

Firestones,  §31,  pl3. 

Fitting  concrete  building  block,  §37,  pp2,  3. 
Flag,  Definition  of,  §32,  p55. 

Flashing  for  roofs,  §42,  p38. 

Flask,  Le  Chatelier,  §35,  p33. 

Flat  spading,  §34,  p47. 

Flemish  bond,  §33,  p5. 
bond,  Double,  §33,  p6. 

Floor  joists  on  building  blocks,  Supporting, 
§37,  p4. 

loads  per  square  foot  of  building,  Table  of 
live,  §14,  pl3. 

loads,  Table  of  reduction  of  live,  §41,  p37. 
Flooring  plaster,  §29,  pl2. 

Floors  in  cities,  Table  of  allowable  live  loads 
on,  §41,  p26. 

Live  load  on  warehouse,  §41,  pl4. 

Weight  of  fireproof,  §41,  pi. 

Flues,  Concrete  blocks  for  chimney,  §37,  p7. 
Flux,  Definition  of,  §40,  p3. 

Follower,  Definition  of,  §39,  p2. 

Footing  on  sloping  ground,  §32,  p49. 

Footings  and  foundations  for  concrete  build¬ 
ing  blocks,  §37,  pi. 

Compound,  §38,  p20. 

Concrete  and  stone,  §32,  p44. 

Design  of  fan-shaped,  §38,  p39. 

Design  of  single,  §38,  p7. 

Fan-shaped,  §38,  p35. 

for  three  or  more  columns,  §38,  p29. 

for  two  columns,  §38,  p22. 

Location  of  center  of  gravity  of  rectangular 
compound,  §38,  p20. 
on  combined  rock  and  gravel,  §32,  p48. 
on  quicksand,  §32,  p47. 

Purpose  of,  §32,  p43. 

Single,  §38,  pi. 

Special,  §32,  p48. 

Spread,  §38,  pi. 

Table  of  safe  load  on  steel  I  beams  used  for, 
§38,  pl5. 

Timber,  §32,  p43. 

Force  of  wind,  Table  of  velocity  and,  §41,  p28. 
Form  work,  Care  of  lumber  for,  §34,  plO. 
Forms,  Construction  of,  §34,  p51. 

Definition  of,  §30,  p29. 

Pilling  of,  §34,  p52. 


Forms — (Continued) 

Stripping  the,  §34,  p52. 

Formula,  Duchemin’s,  §41,  p30. 

Formulas  for  bearing  of  piles,  §39,  p32. 
Foundation  walls,  Thickness  of,  §32,  p54. 

waterproofing,  §42,  p42. 

Foundations  and  columns,  Waterproofing 
through,  §42,  p43. 

for  concrete  building  blocks,  §37,  pi. 
Cantilever,  §38,  p44. 

Design  of  cantilever,  §38,  p50. 

Table  of  safe  loads  of  steel  I  beams  used  for, 
§38,  pl5. 

Foundry  cupola,  §40,  p5. 
pig,  §40,  p5. 

Fragmental,  Example  of,  §31,  p2. 

Friestedt  interlocking  channel  piling,  §39,  p21. 
Freezing  and  wet  weather,  Work  in,  §34,  p52. 
Brard’s  test  of,  §31,  p26. 

Resistance  of  building  stones  to,  §31,  p26. 
weather,  Concreting  in,  §30,  p37. 
weather,  Laying  brick  in,  §33,  pl4. 
weather,  Laying  mortar  in,  §29,  p28. 

Frog,  Definition  of,  §31,  p30. 

Fuller’s  rule  for  quantities  for  concrete, 
§30,  p31. 

Furnace,  Blast,  §40,  p3. 

Puddling,  §40,  p7. 

Reverberatory,  §40,  p7. 
slag  for  concrete,  §30,  pl4. 

G 

Gable  coping,  §32,  p40. 

Galvanized  iron,  §40,  pl7. 

Garden  bond,  §33,  p6. 

Gauge  pile,  §39,  p2. 

Gauged  brick,  §31,  p34. 

Gilbreth  measurer  and  feeder,  §34,  p25. 

rotary  mixer,  §34,  pl6. 

Gillmore  wires,  §35,  p26. 

Glassy  rock,  Example  of,  §31,  p2. 

Glazed  brick,  §31,  p35. 

Gneiss  and  mica  slate,  §31,  p7. 

Grain  and  rift  of  rock,  §31,  p4. 

Granite,  §31,  p5. 
capping,  §39,  pl2. 

Gray,  §31,  p6. 

Red,  §31,  p6. 

used  for  concrete,  Crushed,  §30,  pl3. 
Granular  rock,  Definition  of,  §31,  p2. 
limestone,  §31,  plO. 

Granulometric  composition  of  sand,  §29,  pl6; 
§35,  p31. 

Graphitic  carbon,  §40,  p6. 

Gravel,  Care  of,  §34,  p8. 

Footings  on  combined  rock  and,  §32,  p48. 
for  concrete,  §30,  pl3. 


XVI 


INDEX 


Gravel — (Continued) 

for  concrete  building  blocks,  §36,  pl9; 
§37,  pl3. 

Gravity  concrete  mixer,  §34,  p22. 

Gray  granite,  §31,  p6. 

Greenstone,  §31,  p7. 

Grillage  capping,  §39,  pll. 

Steel-beam,  §38,  po. 

Grillages,  Table  of  safe  load  for  steel  beams 
used  for,  §38,  pl5. 

Grinder  for  stonework,  §32,  po. 

Grout,  Use  of,  §29,  p30. 

Grouting,  Definition  of,  §29,  p30. 

Guide  pile,  §39,  p2. 

Gypsum,  §31,  pl2. 

H 

Hair  cracks,  §32,  p58. 

Half  bat,  §33,  p4. 

Hammer,  Bush,  §32,  p3;  §34,  p54. 

Definition  of,  §39,  p24. 

Double-faced,  §32,  pi. 

Face,  §32,  pi. 

Finishing  concrete  with  pneumatic,  §34,  p55. 
Hand,  §32,  p3. 

Patent,  §32,  p3. 

Peen,  §32,  pi. 

pile  driver,  Drop-,  §39,  p24. 
pile  driver,  Steam-,  §39,  p26. 

Hammers  for  stone,  §32,  pi. 

Hand-cart  mixers,  §34,  p29. 

-drove  work,  §32,  pll. 
finish  for  concrete,  §34,  p54. 

Hangers,  Joist,  §37,  p4. 

Hard  brick,  §31,  p34. 
set,  §35,  p25. 

Hardening,  Definition  of,  §35,  p25. 
of  lime,  §29,  p6. 

Hardness  of  building  stone,  §31,  pi. 

of  rock,  §31,  p3. 

Header,  Definition  of,  §33,  p2. 

Heading  bond,  §33,  p4. 

Heat  on  concrete,  Effect  of,  §30,  p22. 
Hematite,  Composition  of,  §40,  p2. 
Herring-bone  bond,  §33,  p8. 

Heuennekes  system  of  sand-lime  brick  manu¬ 
facture,  §31,  p38. 

High  temperature,  Concreting  at,  §30,  p37. 

temperature,  Laying  brick  at,  §33,  pl4. 
History  of  concrete  building  block,  §36,  pi. 
Hoist,  Bucket,  §34,  p41. 

Hoisting  and  mixing  devices  combined, 
§34,  p43. 
bucket,  §34,  p41. 

Selection  of  method  of,  §34,  p39. 

Hollow  block,  Definition  of,  §36,  p4. 
brick  wall,  §33,  p28. 


Hollow — (Continued) 

walls,  Bonding  of,  §33,  plO. 

Hoppers,  Charging,  §34,  p37. 

Hornstone,  §31,  pll. 

Hot  short,  Cause  of,  §40,  p9. 

weather,  Concreting  in,  §30,  p37. 
weather,  Laying  brick  in,  §33,  pl4. 

Hotels,  Live  loads  for,  §41,  pl3. 

Houses,  Thickness  of  brick  walls  for  dwelling, 
§33,  ppl6,  27. 

Hydrated  lime,  §29,  p3. 

lime  on  concrete  building  blocks,  §36,  p20. 
lime,  Waterproofing  concrete  with,  §42,  p26. 
Hydraulic  cements,  Classification  of  limes  and, 
§29,  p2. 

Definition  of,  §29,  pi. 
index,  §29,  p2. 
lime,  §29,  p3. 

lime,  Classification  of,  §29,  p3. 
limestone,  §31,  pll. 

I 

I  beams,  Table  of  depth,  weight,  and  section 
of  modulus  of  standard,  §38,  pl8. 
beams  used  for  grillages,  Table  of  safe 
load  on  steel,  §38,  pl5. 

Ideal  block  machine,  §36,  p29. 

Improved  cement,  §29,  p7. 

cement,  Manufacture  of,  §29,  p9. 
risk,  §42,  pl6. 

Index,  Hydraulic,  §29,  p2. 

Ingots,  Definition  of,  §40,  pl2. 

Ingredients  for  concrete,  Measuring  and  esti¬ 
mating,  §30,  p31. 

for  concrete,  Proportioning,  §30,  pi 5. 
for  concrete,  Table  of  quantities  of,  §30,  p34. 
in  concrete,  Proportion  of,  §30,  p29. 
in  mortars,  Proportion  of,  §29,  pl8. 
of  cement  mortar,  §29,  p20. 
of  lime  mortars,  §29,  pl8. 

Strength  and  imperviousness  of  concrete 
obtained  by  proportioning,  §30,  pi 5. 
Inspection  of  cement,  Field,  §35,  pi. 

of  cement  required  by  specifications, 
§35,  p36. 

of  materials  for  concrete  blocks,  §36,  p21. 
of  steel  reinforcement,  §34,  p8. 
of  stone  at  quarry,  §31,  p23. 
of  stone  in  buildings,  §31,  p23. 

Instructions  for  operating  a  mixer,  §34,  p31. 

for  starting  and  managing  boilers,  §34,  p33. 
Insurance,  Cost  of  fire,  §42,  pl6. 
engineering,  Definition  of,  §42,  pi. 

Limit  of  fire,  §42,  pl8. 

Purpose  of  fire,  §42,  pi. 

rates,  Adjustment  of  fire,  §42,  pl6. 

rates,  Definition  of,  §42,  pl6.  • 


INDEX 


XVII 


Integral  method  of  waterproofing,  §42,  p25. 
Interlocking  channel  piling,  Friestedt, 
§39,  p21. 

piling,  Nye,  §39,  pl9. 

International  concrete  mixer,  §34,  pl7. 
Inverted  arch,  §32,  p50. 

Iron  and  steel,  General  characteristics  of, 
§40,  pi. 

Best,  §40,  p9. 

Carbon  in  cast,  §40,  p6. 

Characteristics  of  cast,  §40,  p6. 

Common  bar,  §40,  p9. 

Defects  in  wrought,  §40,  p9. 

Definition  of,  §41,  pi. 

Double  best,  §40,  p9. 

from  its  ores,  Separation  of,  §40,  p2. 

Galvanized,  §40,  pl7. 

Ores  of,  §40,  p2. 

Production  of,  §40,  p2. 

Production  of  cast,  §40,  p5. 

Production  of  pig,  §40,  p4. 

Properties  of  wrought,  §40,  p8. 

Purity  of  wrought,  §40,  p7. 

Silicon,  sulphur,  phosphorus,  and  man¬ 
ganese  in  cast,  §40,  p6. 

Strength  of,  §40,  plS. 

Triple  best,  §40,  p9. 

Ironstone,  §31,  pll. 

K 

• 

Keene’s  cement,  §29,  pl3. 

Kerfs,  Definition  of,  §31,  p32. 

Kick,  Definition  of,  §31,  p30. 

King  closer,  §33,  p4. 

Kneeler  for  coping,  §32,  p40. 

Knots,  Definition  of,  §32,  p29. 

L 

Lafarge  cement,  §32,  p29. 

Laws  governing  thickness  of  brick  walls, 
§33,  pl6. 

Le  Chatelier  flask,  §35,  p33. 

Lead,  Strength  of,  §40,  pl8. 

Leads,  Definition  of,  §39,  p24. 

Leaks  in  waterproofing,  §42,  p44. 

Lean  mixture  of  concrete,  §30,  p31. 

Levels  for  field  operations,  §34,  p4. 

Lime,  Air-slaked,  §29,  po. 

-cement  mortar,  §29,  p27. 

Common,  §29,  p2. 

Composition  of,  §29,  p2. 
concrete,  §30,  pi. 

Fat,  §29,  p2. 

for  concrete  blocks,  Hydrated,  §36,  p20. 
Hardening  of,  §29,  p6. 


Lime — (Continued) 

Hydrated,  §29,  p3. 

Hydraulic,  §29,  p3. 

Manufacture  of,  §29,  p4. 

Meager,  §29,  p3. 
mortars,  §29,  pl8. 
mortars,  Mixing,  §29,  pl9. 
mortars,  Strength  of,  §29,  p20. 
mortars,  Use  of,  §29,  pi 9. 

Poor,  §29,  p3. 

Properties  of,  §29,  p5. 

Rich,  §29,  p2. 

Water  required  to  slake,  §29,  p5. 

Limes  and  hydraulic  cements,  Classification 
of,  §29,  p2. 

Limestone,  §31,  p9. 

Argillaceous,  §31,  plO. 

Cherty,  §31,  pll. 

Compact,  §31,  plO. 

Crystalline,  §31,  plO. 

Ferruginous,  §31,  plO. 

for  concrete,  Broken,  §30,  pl4. 

Granular,  §31,  plO. 

Hydraulic,  §31,  pll. 

Magnesian,  §31,  plO. 

Oolitic,  §31,  plO. 

Shelly,  §31,  plO. 

Silicious,  §31,  plO. 

Lintel,  Beam  support  for,  §32,  p36. 

Built-up,  §32,  p37. 

Relieving,  §32,  p35. 

Stone,  §32,  p34. 

Lintels,  Concrete  building  blocks  for,  §37,  p8. 
Live  load,  Definition  of,  §41,  pi 3. 

load  on  floors  in  various  cities,  Table  of 
allowable,  §41,  p26. 

load  per  square  foot  in  various  buildings, 
Table  of,  §41,  pl3. 

loads  from  floor  to  floor,  Table  of  reduction 
of,  §41,  p37. 

loads  on  warehouse  floors,  §41,  pl4. 

Load,  Dead,  §41,  pi. 

for  steel  beams  used  for  grillages,  Table  of 
safe,  §38,  pl5. 

on  roof  trusses,  Dead,  §41,  p9. 

Snow,  §41,  p27. 

Wind,  §41,  p27. 

Loading,  Rate  of,  §35,  p23. 

Loads,  Disposition  of,  §41,  p35. 

from  floor  to  floor,  Table  of  reduction  ot 
live,  §41,  p37. 

Limnoria,  §39,  p2. 

Low  temperature,  Concreting  at,  §30,  p37. 
temperature,  Laying  brick  at,  §33,  pl4. 
temperature,  Working  at,  §34,  p52. 

Lug  sill,  §32,  p38. 

Lumber  for  form  work,  Care  of,  §34,  plO. 


XV111 


INDEX 


M 

Machine-drove  work,  §32,  pll. 

-made  brick,  §31,  p31. 

tools  for  stone  cutting,  §32,  p4. 

Magnetite,  Composition  of,  §40,  p2. 
Magnesian  limestone,  §31,  plO. 

Mallet  for  stone  cutting,  §32,  p3. 

Manganese  bronze,  Composition  of,  §40,  p20. 
in  cast  iron,  §40,  p6. 
steel,  §40,  pl5. 

Marble,  §31,  pll. 

Marbles,  Brecciated,  §31,  pl2. 

Margins,  Definition  of,  §32,  p6. 

Masonry,  Ashlar,  §32,  p21. 

Care  of  stone,  §32,  p28. 

Cleaning  stone,  §32,  p29. 

Defective  methods  of  building  stone, 
§32,  pl6. 

Laying  of  stone,  §32,  p30. 

Pointing,  §29,  p29. 

Pointing  stone,  §32,  p28. 

Rubble,  §32,  pl7. 

Strength  of  stones  and,  §31,  pl8. 

Table  of  allowable  stresses  in  brick, §31, p41. 
Table  of  strength  of  brick,  §31,  p41. 

Mat,  Definition  of,  §40,  p8. 

Matrix,  Definition  of,  §30,  pi. 

Meager  lime,  §29,  p3. 

Measurer  and  feeder,  Gilbreth,  §34,  p25. 
Measuring  and  estimating  ingredients  for  con¬ 
crete,  §30,  p31. 

ingredients,  Fuller’s  rule  for,  §30,  p31. 
Medium  concrete,  §37,  pi 4. 

mixture  of  concrete,  §30,  p30. 

Membrane  method  of  waterproofing,  §32,  p32. 
Merchandise,  Table  of  weights  of,  §41,  pl6. 
Metal  bearing  pile,  §39,  pl4. 

ties  for  bonding,  §33,  p9. 

Metals,  Table  of  ultimate  strength  of,  §40,  pl8. 
Mica  slate,  Gneiss  and,  §31,  p7. 

Microscopic  examination  of  stone,  §31,  p24. 
Mill  construction,  §42,  plO. 

Minwax  waterproofing  compound,  §42,  p30. 
Miracle  block  machine,  §36,  p29. 

Mixed  cement,  §29,  p7. 

Mixer,  Carlin  cube,  §34,  pl3. 

Cockbum  concrete,  §34,  p21. 

‘  Drake,  §34,  p20. 

Gilbreth  rotary,  §34,  pl6. 

Gravity  concrete,  §34,  p22. 

International  concrete,  §34,  pl7. 

Ransome  concrete,  §34,  pi 4. 

Smith,  §34,  pl6. 

Mixers,  Concrete  batch,  §34,  pll. 

Continuous  concrete,  §34,  ppll,  19. 

Cube  concrete,  §34,  pll. 
for  concrete,  §34,  plO. 


Mixers — (Continued) 

Hand-cart,  §34,  p29. 

Operation  of  concrete,  §34,  p31. 

Power  equipment  for  concrete,  §34,  p27. 
Quantitative  concrete,  §34,  ppll,  24. 
Mixing  cement  mortar,  §29,  p23. 

concrete  blocks  by  machinery,  §36,  p26. 
concrete  building  blocks,  §36,  pl7. 
concrete  building  blocks  by  hand,  §36,  p25. 
concrete  to  make  it  waterproof,  §42,  p25. 
devices,  Combined  hoisting  and,  §34,  p43. 
lime  mortars,  §29,  pl9. 
of  concrete,  §30,  p33. 
of  fine  facing,  §36,  p27. 

Mixture,  Consistency  of  concrete,  §30,  p29. 
of  concrete,  Common,  §30,  p30. 
of  concrete,  Lean,  §30,  p31. 
of  concrete,  Medium,  §30,  p30. 
of  concrete,  Rich,  §30,  p30. 

Modulus  of  elasticity  of  metals,  §40,  pl8. 
of  rupture  of  brick,  §31,  p39. 
of  rupture  of  building  stone,  §31,  p20. 
of  rupture  of  concrete,  §30,  pp25,  27. 
of  rupture  of  concrete  blocks,  §36,  pl2. 
of  rupture  of  metals,  §40,  pl8. 

Mold,  Face-down,  §36,  pp27,  29. 

Face-up,  §36,  p27. 

Side-face,  §36,  pp27,  29. 

Molded  brick,  §31,  pp33,  34. 

Molding,  Dry,  §31,  p30. 

Slop,  §31,  p30. 

Molds  for  briquet,  §35,  pl7. 

Mooring  pile,  §39,  pi. 

Morse  patent  tie,  §33,  pl2. 

Mortar,  Abrasive  strength  of  cement,  §29,  p26. 
Adhesive  strength  of  cement,  §29,  p26. 
barrow,  Tray,  §34,  p37. 

Cement,  §29,  p20;  §30,  p2. 

Compressive  strength  of  cement,  §29,  p26. 
Definition  of,  §30,  pi. 

for  concrete  building  blocks,  Composition 
of,  §37,  p3. 

in  freezing  weather,  Laying,  §29,  p28. 
Ingredients  of  cement,  §29,  p20. 
joints  for  concrete  building  blocks,  §37,  p2. 
joints,  Thickness  of,  §33,  pl5. 

Lime-cement,  §29,  p27. 

Mixing  cement,  §29,  p23. 

Retempering  cement,  §29,  p27. 

Shrinkage  of  cement,  §29,  p28. 

Strength  of  cement,  §29,  p25. 

Strength  of  sand,  §29,  pi 7. 

Table  of  materials  required  per  cubic  yard 
of  cement,  §29,  p23. 

Tensile  strength  of  cement,  §29,  p26. 
tests,  Sand  for,  §35,  pl6. 

Mortars,  Coloring  of  cement,  §29,  p31. 


INDEX 


xix 


Mortars — (Continued) 

Composition  of,  §29,  pl8. 

Consistency  of  sand,  §35,  pl4. 

Lime,  §29,  pl8. 

Properties  of  cement,  §29,  p25. 

Proportion  of  ingredients  in  cement, 
§29,  P21, 

Strength  of  lime,  §29,  p20. 

Table  of  tensile  strength  of  cement,  §29,  p25. 
Waterproofing  of  cement,  §29,  p30. 

N 

Natural  and  slag  cement,  Tests  of,  §35,  p36 
cement,  §29,  p6;  §36,  pl8. 

Neat  cement,  §30,  pi. 

Needle,  Vicat,  §35,  p25. 

Nickel  steel,  §40,  pl6. 

Night  work,  §34,  p53. 

Nipper,  Definition  of,  §39,  p26.  • 
Non-staining  cement,  §29,  pl3. 

Normal  consistency  of  cement,  §35,  pl4. 
tests  of  cement,  §35,  p7. 
wind  pressure,  Table  of,  §41,  p30. 

Nye  interlocking  piling,  §39.,  pl9 

O 

One-piece  concrete  building  block,  §36,  p4. 
Oolitic,  Definition  of,  §31,  p3. 

limestone,  §31,  plO. 

Open-hearth  process,  §40,  plO. 

Ordinarily  hydraulic  lime,  §29,  p3. 

Ores  of  iron,  §40,  p2. 

Separation  of  iron  from  its,  §40,  p2. 
Organization  of  working  force,  §34,  p3. 
Ozocerite,  Definition  of,  §42,  p30. 

P 

Pale  brick,  §31,  p33. 

Pan,  Dry,  §31,  p32. 

Paraffin  to  waterproof  concrete,  §42,  p30. 
Parian  cement,  §29,  pl3. 

Paris,  Plaster  of,  §31,  pi 2;  §29,  pl2. 
Partitions,  Concrete  building-block,  §37,  p6. 
Party  wall,  Brick,  §33,  p28. 

Patent  hammer,  §32,  p3. 

-hammered  work,  §32,  pl3. 

Paving  brick,  §31,  p36. 

Pebbles  for  concrete,  §30,  pl3. 

Peen  hammer,  §32,  pi. 

Perpends,  Keeping  the,  §33,  p2. 

Philippine  woods,  Table  of  weight  of,  §41,  p25. 
Phosphor  bronze.  Composition  of,  §40,  p20. 
Phosphorus  in  cast  iron,  §40,  p6. 

Pick  for  stone  cutting,  §32,  pi. 

Picked  work,  §32,  p4. 

Pier  construction,  Compressol  system  of  con¬ 
crete-,  §39,  p57. 


Pig,  Foundry,  §40,  p5. 

iron,  Production  of,  §40,  p4. 

Pilaster  in  concrete-block  wall,  §37,  p5. 

Pile,  Anchor,  §39,  pi. 

Bearing,  §39,  pi. 

by  hammer,  Driving  Raymond  concrete 
§39,  p42. 

by  water  jet,  Driving  Raymond,  §39,  p44. 
Cast-iron,  §39,  pl4. 

Chenoweth  concrete,  §39,  p56. 

Close,  §39,  p2. 

Construction,  Compressol  system  of  con¬ 
crete-,  §39,  p57. 

•  Corrugated  concrete,  §39,  p53. 

Disk,  §39,  pl4. 
driver,  §39,  p24. 

driver,  Comparison  of  drop-  and  steam* 
hammer,  §39,  p27. 
driver,  Drop-hammer,  §39,  p24. 
driver,  Location  of,  §39,  p28. 
driver,  Steam-hammer,  §30,  p26. 

Driving  of  inclined,  §39,  p28. 

Filling,  §39,  p2. 

Follower,  §39,  p2. 

Gauge,  §39,  p2. 

Guide,  §39,  p2. 

Metal  bearing,  §39,  pl4. 

Pneumatic,  §39,  pi 5. 

Raymond  concrete,  §39,  p42. 

Sand,  §39,  pl3. 

Screw,  §39,  pl4. 

Sheet,  §39,  pl6. 

Simplex  concrete,  §39,  p46. 

Simplex  molded  concrete,  §39,  p48. 

Simplex  shell  concrete,  §39,  p50. 

Simplex  wharf  concrete,  §39,  p50. 

Strength  of,  §39,  p29. 

Test,  §39,  p2. 

Wakefield,  §39,  pl8. 

Piles,  Advantages  of  concrete,  §39,  p35. 
Bearing  of  screw  and  disk,  §39,  p34. 
Capping  of,  §39,  pll. 

Capping  of  concrete,  §39,  p38. 

Classification  of,  §39,  pi. 

Composite,  §39,  p51. 

Cost  of  wood  and  concrete,  §39,  pp59,  60. 
Engineering  News  formula  for,  §39,  p32. 
Factor  of  safety  for,  §39,  p33. 

Formula  for  bearing  power  of,  §39,  p32. 
Lateral  movement  of,  §39,  pl3. 

Method  of  construction  of  concrete,  §39,  p35. 
Method  of  driving,  §39,  p23. 

Protection  of,  §29,  pi ;  §39,  7. 
Reinforcement  of  concrete,  §39,  p64. 
Selection  of,  §39,  pll. 

Shoeing  of,  §39,  p4. 

Soils  best  suited  for  concrete,  §39,  p37. 


XX 


INDEX 


Piles —  (Con  tinued) 

Spacing  of,  §39,  pll. 

Splicing  of,  §39,  p4. 

Strength  of  bearing,  §39,  p29. 

Strength  of  concrete,  §39,  p62. 

Table  of  formulas  for  bearing  of,  §39,  p34. 
Wooden  bearing,  §39,  p2. 

Piling,  Concrete,  §39,  p35. 

Friestedt  interlocking  channel-bar,  §39,  p21. 
Jackson,  §39,  p21. 

Nye  interlocking,  §39,  pl9. 

Reinforced -concrete  sheet,  §39,  p65. 

Steel  sheet,  §39,  pl8. 

Strength  of  sheet,  §39,  p29. 

Terms  used  in,  §39,  p2. 

United  States  steel  sheet,  §39,  p22. 
Wemlinger.  §39,  p23. 

Wooden  sheet,  §39,  pl6. 

Pipe  connections,  Waterproofing  around, 
§42,  p44. 

Pisolitic,  Definition  of,  §31,  p3. 

Pit  sand,  §29,  pi 4. 

Pitch,  Definition  of,  §42,  p34. 

-lake  asphalt,  Trinidad,  §42,  p34. 
of  roof  trusses,  §41,  p7. 

Qualities  of,  §42,  p34. 

Pitched-faced  work,  §32,  p5. 

Pitching  chisel,  §32,  p4. 

Planer  for  stone  work,  §32,  p4. 

Planes  of  slaty  cleavage,  §31,  p9. 

Plans,  Examination  and  care  of,  §34,  p2. 
Plaster,  Composition  of,  §29,  pl2. 

Flooring,  §29,  pl2. 
of  Paris,  §29,  pl2;  §31,  pl2. 

WaU,  §29,  pl2. 

Plug,  Metal  nailing,  §38,  p6. 

Pneumatic  pile,  §39,  pl5. 

Point  for  stone  cutting,  §32,  p4. 

Pointed  work,  §32,  p6. 

Pointing  masonry,  §29,  p29. 

stone  masonry,  §32,  p28. 

Poor  lime,  §29,  p3. 

Porous  terra  cotta,  §31,  p37. 

Porphyritic,  Definition  of,  §Sl,  p2. 

Portable  gravity  concrete  mixer,  §34,  p22. 
Portland  cement,  §29,  p6;  §36,  pl8. 
cement,  Second-grade,  §29,  p9. 
cement,  White,  §36,  pl9. 

Power  equipment  for  concrete  mixers,  §34,  p27. 

tampers,  §36,  p34. 

Premiums,  Definition  of,  §42,  pl6. 

Pressed  brick,  §31,  pp33,  34. 

Pressure  of  wind,  §41,  p27. 

Table  of  normal  wind,  §41,  p30. 

Primary  cement  tests,  §35,  pp4,  5. 

Principles,  Definition  of,  §41,  p9. 
Proportioning  concrete  by  voids,  §30,  pi 7. 


Proportioning —  (Continued) 
concrete  by  weight,  §30,  pl8. 
ingredients  for  concrete,  §30,  pl5. 
materials  for  building  blocks,  §36,  p22. 
Protection,  Private  fire,  §42,  pi 4. 

Public  fire,  §42,  pi 5. 

Puddling  furnace,  §40,  p7. 

Method  of,  §40,  p8. 
process,  §40,  p7. 

Pug  mill,  §31,  p32. 

Purity  of  wrought  iron,  §40,  p7. 

Puzzolan  cement,  §29,  p7 ;  §36,  pl8. 
Puzzuolana,  Definition  of,  §29,  pp6,  7. 

Q 

Quantitative  concrete  mixers,  §34,  ppll,  24. 
Quarry,  Inspection  of  stone  at,  §31,  p23. 
Quarrying  and  finishing  building  stone.  Effect 
of,  §31,  pl7. 

Quarter  bat,  §33,  p4. 

Quartz,  Arenaceous,  §31,  pl3. 

Queen  closer,  §33,  p4. 

Quicksand,  Placing  footings  on,  §32,  p47. 
Quicklime,  §31,  pl2. 

Definition  of,  §29,  p2. 

Quoin,  Stone,  §32,  p32. 

Quoins,  Concrete  building  blocks  for,  §37,  p7. 
Walls  with  brick,  §32,  p20. 

R 

Rabbling,  Definition  of,  §40,  p8. 

Rainy  weather,  Working  in,  §34,  p52 
Random-coursed  ashlar,  §32,  p24. 

Ransome  concrete  mixer,  §34,  pl4. 

hand  concrete  mixer,  §34,  p29. 

Rate  of  loading,  §35,  p23. 

Rates,  Adjustment  of  fire-insurance,  §42,  pl6. 
Raymond  concrete  pile,  §39,  p42. 

concrete  pile  by  hammer,  Driving,  §39,  p42. 
concrete  pile  by  water  jet,  Driving,  §39,  p44. 
Recarburizing,  Definition  of,  §40,  pl2. 

Red  brick,  §31,  p34. 
granite,  §31,  p6. 

hematite,  Composition  of,  §40,  p2. 
short,  Cause  of,  §40,  p9. 

Reduction  of  live  loads  from  floor  to  floor, 
Table  of,  §41,  p37. 
process,  §40,  p3. 

Refusal,  Definition  of,  §39,  p33. 

Regulations  in  various  cities  for  the  allowable 
stress  in  concrete,  Table  of,  §30,  p26. 
Reinforced-concrete  fireproof  construction, 
§42,  pl3. 

-concrete  sheet  piling,  §39,  p65. 
Reinforcement,  Inspection  of  steel,  §34,  p8. 
Machinery  for  bending  steel,  §34,  p48. 
of  concrete  piles,  §39,  p64. 


INDEX 


xxi 


Reinforcement — (Continued) 

Tools  for  bending  steel,  §34,  p49. 
Reinforcing  steel  twisting  machine,  §34,  p48. 
Relieving  lintel,  §32,  p35. 

Retempering  cement  mortar,  §29,  p27. 

concrete,  §30,  p36. 

Reverberatory  furnace,  §40,  p7. 

R.  I.  W.  waterproofing  compound,  Toch’s, 
§42,  p29. 

Ribs  in  slate,  Definition  of,  §31,  p9. 

Rich  lime,  §29,  p2. 

mixture  of  concrete,  §30,  p30. 

Rift  and  grain  of  rock,  §31,  p4. 

Risk,  Definition  of,  §42,  pl6. 

Improved,  §42,  pl6. 

River  gravel  for  concrete,  §30,  pl3. 
sand,  §29,  pl4. 

Rock,  Aggregation  of  particles  of,  §31,  p3. 
and  gravel,  Footings  on  combined,  §32,  p48. 
Color  of,  §31,  p4. 

-faced  work,  §32,  po. 

Grain  and  rift  of,  §31,  p4. 

Structure  of,  §31,  p2. 

Rods,  Tools  for  bending,  §34,  p49. 

Rollers  for  concrete,  §34,  p47. 

Rolling,  Method  of,  §40,  p8. 

Roman  cement,  §29,  p8. 

Roof  covered  with  tile  or  brick,  §42,  p37. 
over  concrete,  Specifications  for  coal-tar 
pitch  and  felt,  §42,  p36. 
plates  on  concrete  building  blocks,  Fasten¬ 
ing,  §37,  p5. 

trusses,  Dead  load  of,  §41,  p9. 
trusses,  Table  of  weight  of,  §41,  pl2. 
Waterproofing,  §42,  p35. 
waterproofing,  Data  for  estimating,  §42,  p37. 
Roofs,  Flashing  for,  §42,  p38. 

Expansion  joints  of  vitrified-tile  or  brick, 
§42,  p40. 

Rosendale  cement,  §29,  p8. 

Rotary  mixer,  Gilbreth,  §34,  pl6. 
Rottenstone,  §31,  pll. 

Rubble,  Coursed,  §32,  p20. 

walls,  §32,  pl8. 

Rubblework,  §32,  pi 7. 

Rough-pointed  work,  §32,  p6. 

Rubbed  work,  §32,  pll. 

Rules  for  operating  concrete  mixers,  §34,  p31. 
for  quantities  for  concrete,  Fuller’s,  §30,  p31. 
for  starting  and  managing  boilers,  §34,  p33. 
Running  bond,  §33,  p6. 

Rusticated  work,  §32,  pl5. 

8 

Safe  loads  for  steel  I  beams  used  for  grillages, 
Table  of,  §38,  pi 5. 
stresses  for  brick  masonry,  §31,  p41. 


stresses  in  stones  and  masonry,  §31,  pl8. 
Safety  factor  for  piles,  §39,  p33. 

factor  used  for  masonry,  §31,  p21. 

Salmon  brick,  §31,  pp33,  34. 

Salt  for  concrete  building  blocks,  §36,  p21. 
Sampling  of  cement,  §35,  p3. 

Sand-blast  finish,  §34,  p55. 

Care  of,  §34,  p8. 
cement,  §29,  pp7,  9. 

Coarse,  §29,  pl6. 

Composition  of,  §29,  pi 4. 

Fine,  §29,  pl6. 

for  building  blocks,  §36,  pl9;  §37,  pl3. 
for  mortar  tests,  §35,  pl6. 
grains,  Shape  of,  §29,  pl5. 

Granulometric  composition  of,  §29,  pl6; 
§35,  p31. 

holes  in  stonework,  §32,  p30. 

-lime  brick,  Manufacture  of,  §31,  p38. 
mortar,  Strength  of,  §29,  pl7. 
mortars,  Consistency  of,  §35,  pi 4. 
Manufacture  of,  §29,  pi 7. 

Percentage  of  voids  in,  §29,  pl5. 

Pit,  §29,  pl4. 

Preparation  of,  §29,  pl7. 

Purity  of,  §29,  pl7. 

River,  §29,  pl4. 

Sea,  §29,  pl4. 

Selection  of,  §36,  p22. 

Specific  gravity  of,  §29,  pl5. 

Testing  of,  §29,  pl5. 

Uses  of,  §29,  pl4. 

Weight  of,  §29,  pl5. 

Sand  pile,  §39,  pl3. 

Sandstone,  §31,  p7. 

Sap,  Definition  of,  §32,  p29. 

Saturated  felt,  §42,  p35. 

Saw,  Band,  §32,  p4. 

Circular,  §32,  p4. 

Drag,  §32,  p4. 

Scale  work,  §32,  pl3. 

Schistose  rock,  Definition  of,  §31,  p2. 

Schwarz  system  of  sand-lime  brick  manufac¬ 
ture,  §31,  p38. 

Scoria  used  in  cement  manufacture,  §29,  p9. 
Screenings,  Definition  of,  §37,  pi 4. 

Screw  and  disk  pile,  Bearing  of,  §39,  ppl4,  34. 

conveyer,  §31,  p31. 

Seasoning  cement,  §35,  p6. 

Second-grade  Portland  cement,  §29,  p9. 
Section  modulus  of  standard  I  beams,  Table 
of  depth,  weight,  and,  §38,  pl5. 
Semiporous  terra  cotta,  §31,  p37. 

Set,  Definition  of,  §29,  pi. 

Hard,  §35,  p25. 

Initial,  §35,  p25. 

Setting,  Definition  of,  §35,  p24. 


XXII 


INDEX 


Setting — (Continued) 

test,  Apparatus  for  time  of,  §35,  p25. 
test,  Reason  for  time  of,  §35,  p24. 
tests,  Result  of  time  of,  §35,  p27. 

Time  of,  §35,  pp4,  24. 

Shale  for  concrete,  §30,  pl4. 

Shaly  rock  for  concrete,  §30,  pl4. 

Shear  steel,  §40,  pl4. 

Shearing  strength  of  concrete,  §30,  p27. 
strength  of  metals,  §40,  pl8. 
stress  of  concrete,  Allowable,  §30,  p25. 
Sheet-metal  concrete  carts,  §34,  p34. 
pile,  §39,  pl6. 

piling,  Reinforced-concrete,  §39,  p65. 
piling,  Steel,  §39,  pl8. 
piling,  Strength  of,  §39,  p29. 
piling,  United  States  steel,  §39,  p22. 
piling,  Wood,  §39,  pl6. 

Shell  concrete  pile,  Simplex,  §39,  p50. 
Shelly  limestone,  §31,  plO. 

Shoeing  of  piles,  §39,  p4. 

Shrinkage  of  cement  mortar,  §29,  p29. 

of  concrete,  §30,  p21. 

Side-face  mold,  §36,  pp27,  29. 

Sidewalk  construction,  §32,  p55. 

Brick,  §32,  p57. 

Cement,  §32,  p57. 

Stone,  §32,  p56. 

Silica  cement,  §29,  p9. 

Silicious  limestone,  §31,  plO. 

stones,  §31,  p5. 

Silicon  in  cast  iron,  §40,  p6. 

Sill,  Lug,  §32,  p38. 

Slip,  §32,  p38. 

Stone,  §32,  p38. 

Sills,  Concrete  building  blocks  for,  §37,  p8. 
Simplex  concrete  pile,  §39,  p46. 
molded  concrete  pile,  §39,  p48. 
shell  concrete  pile,  §39,  p50. 
wharf  concrete  pile,  §39,  p50. 

Single  footings,  §38,  pi. 

footings,  Design  of,  §38,  p7. 
shear  steel,  §40,  pl5. 

Skeleton  construction,  §41,  p38. 

steel  construction,  Fireproof,  §42,  pl2. 
Slag  cement,  §29,  p9. 

cement,  Tests  of  natural  and,  §35,  p36. 
Definition  of,  §40,  p3. 
for. concrete,  §30,  pl4. 
olake,  Definition  of,  §29,  pp4,  5. 

Slake  lime,  Water  required  to,  §29,  p5. 
Slate,  §31,  p9. 

Definition  of  ribs  or  vein  in,  §31,  p9. 
for  concrete,  §30,  pl5. 

Gneiss  and  mica,  §31,  p7. 

Slice  bar,  §34,  p47. 

Slip,  Definition  of,  §31,  p35. 


Sli  p —  (Continued) 
joint,  §33,  pl4. 
sill,  §32,  p38. 

Slop  molding,  §31,  p30. 

Sloping  ground,  Footing  on,  §32,  p49. 
Slow-burning  construction,  §42,  plO. 

Smith  mixer,  §34,  pl6. 

Snow  load,  §41,  p27. 

Soft  brick,  §31,  p34. 

-mud  process,  §31,  p31. 

Soils  best  suited  for  concrete  piles,  §39,  p37. 
Solid  brick  wall,  §33,  p28. 

Soundness  of  cement,  §35,  pp4,  5. 

of  cement,  Determination  of,  §35,  p6. 
of  cement,  Results  of  tests  of,  §35,  pl3. 
Spade  for  placing  concrete,  §34,  p47. 

Spading,  Flat,  §34,  p47. 

Specific  gravity  of  building  stone,  §31,  p28. 

V  gravity  of  sand,  §29,  pl5. 

-gravity  test,  Apparatus  for,  §35,  p33. 
-gravity  test,  Method  of  making,  §35,  p33. 
-gravity  test,  Reasons  for,  §35,  pp4,  32. 
-gravity  tests,  Results  of,  §35,  p34. 
Specifications,  Barrett,  §42,  p36. 

for  coal-tar  pitch  and  felt  roof  over  con¬ 
crete,  §42,  p36. 

for  concrete  building  blocks,  §37,  pl3. 
for  Portland  cement,  §35,  p36. 
for  roof  covered  with  tile  or  brick, 
§42,  p37. 

for  subsurface  waterproofing,  §42,  p42. 
Sphaeroma,  §39,  p2. 

Splicing  of  piles,  §39,  p4. 

Spot-faced,  Definition  of,  §39,  pl2. 

Spread  footing,  Table  of  safe  load  of  steel 
beams  used  for,  §38,  pl5. 
footings,  §38,  pi. 
footings,  Advantage  of,  §38,  pi. 
footings,  Design  of  single,  §38,  p7. 
Spreading  of  fires,  §42,  p7. 

of  fires,  Causes  of,  §42,  p8. 

Sprinklers,  Automatic,  §42,  pl4. 

Squeezer,  Definition  of,  §40,  p8. 

Stair,  Stone,  §32,  p42. 

Steam  curing,  §37,  pl6. 

-hammer  pile  driver,  §39,  p26. 

-hammer  pile  driver,  Drop-  and,  §39,  p27. 
test  of  cement,  §35,  pl3. 

Stearates  for  waterproofing  concrete,  §42,  p28. 
Steel,  Alloy,  §40,  pl5. 

-beam  grillage,  §38,  p5. 

Blister,  §40,  pl4. 

Comparative  value  of  the  several  different 
classes  of,  §40,  pi 3. 

Definition  of,  §40,  plO;  §41,  pi. 

frame  construction,  Fireproof,  §42,  pl2. 

General  characteristic  of  iron  and,  §40,  pi. 


INDEX 


xxm 


Steel — (Continued) 

I  beams  used  for  grillages,  Table  of  safe 
loads  on,  §38,  pl5. 
in  concrete,  Corrosion  of,  §30,  p20. 
Machinery  for  bending,  §34,  p48. 
Manganese,  §40,  pl5. 

Manufacture  of,  §40,  plO. 

Nickel,  §40,  pl6. 

reinforcement,  Inspection  of,  §34,  p8. 
Shear,  §40,  pl4. 
sheet  piling,  §39,  pl8. 
stirrups,  §37,  p4. 

Strength  of,  §40,  pl8. 

Tools  for  bending,  §34,  p49. 

Tungsten,  §40,  pl5. 
twisting  machine,  §34,  p48. 

Step,  Stone,  §32,  p41. 

Stereotomy,  Definition  of,  §32,  p5. 

Stiff-mud  process,  §31,  p32. 

Stirrups,  Steel,  §37,  p4. 

Stock  board,  §31,  p30. 
brick,  §31,  p34. 

Stone  at  quarry,  Inspection  of,  §31,  p23. 
Bending  strength  of  building,  §31,  p27. 
Bond,  §32,  p31. 

Care  of,  §34,  pS. 

Chemical  analysis  of  building,  §31,  p24. 
Classification  of  building,  §31,  p5. 
concrete,  Definition  of,  §30,  p2. 
coping,  §32,  p39. 

Crushing  strength  of  building,  §31,  p27. 
cutting  and  finishing,  §32,  pi. 
cutting  tools,  §32,  pi. 
defects,  §32,  p29. 

Density  of  building,  §31,  pi. 

Durability  of  building,  §31,  pl4. 

Effect  of  climate  and  environment  on  build¬ 
ing,  §31,  pl5. 

Effect  of  fire  on  building,  §31,  pl8. 

Effect  of  quarrying  and  finishing  on, 
§31,  pl7. 

Faults  in  dressing,  §32,  p30. 
for  ashlar.  Best,  §32,  p26. 
for  concrete  building  blocks,  §36,  pl9; 
§37,  pl3. 

for  concrete,  Comparative  values  of, 
§30,  pll. 

for  concrete,  Desirable  properties  of,  §30,  p3. 
for  concrete,  Size  of,  §30,  p3. 
footings  and  concrete,  §32,  p44. 
hammers,  §32,  pi. 

Hardness  of  building,  §31,  pi. 
in  buildings,  Inspection  of,  §31,  p23. 

Jamb,  §32,  p32. 

Laboratory  tests  of  building,  §31,  p23. 

lintel,  §32,  p34. 

lintel,  Built-up,  §32,  p37. 


Stone — (Continued) 

masonry,  Cleaning,  §32,  p29. 
masonry,  Defective  building  of,  §32,  pl6. 
masonry,  General  considerations  of,  §32,  pl5. 
masonry,  Laying  of,  §32,  p30.  H 
masonry,  Pointing,  §32,  p28. 

Methods  of  testing  building,  §31,  p25. 
Microscopic  examination  of  building, 
§31,  p24. 

on  strength  of  concrete,  The  effect  of  the 
size  of,  §30,  p9. 

Permanence  of  color  of  building,  §31,  p27. 
Physical  properties  of  building,  §31,  pi. 
Physical  structure  of  building,  §31,  pl4. 
Physical  tests  of  building,  §31,  p24. 
quoin,  §32,  p32. 
rubble  walls,  §32,  pl8. 
sidewalks,  §32,  p56. 
sill,  §32,  p38. 

Specific  gravity  of  building,  §31,  p28. 
stair,  §32,  p42. 
step,  §32,  p41. 

Table  of  durability  of  building,  §31,  pl7. 
Table  showing  the  compressive  strength  of 
concrete  made  of  different-sized,  §30,  plO. 
templet,  §32,  p31. 

to  acids,  Resistance  of  building,  §31,  p27. 
to  fire,  Resistance  of  building,  §31,  p29. 
trimmings,  §32,  p31. 
wall,  Thickness  of,  §32,  p54. 
walls  with  brick  quoins,  §32,  p20. 

Stones,  Absorptive  power  of  building,  §31,  p25. 
and  masonry,  Strength  of,  §31,  pl8. 
Silicious,  §31,  p5. 

Selection  of  building,  §31,  p22. 
to  abrasion,  Resistance  of  building,  §31,  p26 
to  freezing,  Resistance  of  building,  §31,  p26. 
used  in  concrete.  Table  of  comparative 
values  of,  §30,  pl2. 

Stonework,  Care  of,  §32,  p28. 

-work,  Finish  of,  §32,  p5. 

Stratified,  Definition  of,  §31,  p2. 

Stress  in  concrete  allowed  by  various  cities. 
Table  of,  §3.0,  p26. 

Stresses  of  concrete,  Working,  §30,  p24. 
Stretcher,  Definition  of,  §33,  pi. 

Stretching  bond,  §33,  p5. 

Stripping  the  forms,  §34,  p.52. 

Structure  of  building  stone,  Physical,  §31,  pl4;j 
of  rock,  §31,  p2. 

Stucco,  §29,  pi  2.  ■,( 

Subsurface  waterproofing,  §42,  p41. 

Sulphur  in  cast  iron,  §40,  p6. 

Superficial  method  of  waterproofing  concrete 
§42,  p29. 

Superintendent,  Duties  of  the,  §34,  pi. 

Notes  for  the,  §34,  p51. 


211—46 


XXIV 


INDEX 


Syenite,  §31,  p6. 

Sylvester  process  of  waterproofing  concrete, 
§42.  p28. 

T  - 

Table  of  absorptive  power  of  stones,  §31,  p25. 
of  allowable  live  loads  on  floors  in  cities, 
§41,  p26. 

of  allowable  unit  stresses  for  brick  masonry, 
§31,  p41. 

of  allowable  unit  stresses  in  masonry 
materials,  §31,  p21. 

of  comparative  values  of  different  aggre¬ 
gates  used  in  concrete,  §30,  pl2. 
of  compressive  strength  of  concrete  with 
the  different-sized  aggregates,  §30,  plO. 
of  depth,  weight,  and  section  modulus  of 
standard  I  beams,  §38,  pl8. 
of  durability  of  building  stone,  §31,  pl7. 
of  fire  record  of  various  cities,  §42,  p3. 
of  formulas  for  bearing  of  piles,  §39,  p34. 
of  live  loads  per  square  foot  in  different 
buildings,  §41,  pl3. 

of  materials  required  per  cubic  yard  of 
cement  mortar,  §29,  p23. 
of  normal  wind  pressure,  §41,  p30. 
of  quantities  of  ingredients  for  mixing  con¬ 
crete,  §30,  p34. 

of  reduction  of  live  loads  from  floor  to  floor, 
§41,  p37. 

of  requirements  for  cements,  §35,  p37. 
of  safe  load  on  I  beams  used  for  foundation 
grillages,  §38,  pl5. 

of  specific  gravity  and  weight  of  building 
stone,  §31,  p28. 

of  strength  of  brickwork,  §31,  p4. 
of  strength  of  brick  and  terra  cotta, 
§31,  p40. 

of  strength  of  cement  briquet,  §35,  p23. 
of  strength  of  stones  and  masonry, 
§31,  P20. 

of  tensile  strength  of  Portland  cement 
mortars,  §29,  p25. 

of  thickness  of  brick  walls  for  dwelling 
houses,  §33,  p27. 

of  thickness  of  brick  walls  for  warehouses 
and  storage  houses,  §33,  p22. 
of  thickness  of  foundation  walls,  §32,  p54. 
of  ultimate  strength  of  concrete,  §30,  p28. 
of  ultimate  strength  of  metals,  §40,  pl8. 
of  unit  working  values  of  concrete  allowed 
by  various  cities,  §30,  p26. 
of  velocity  and  force  of  wind,  §41,  p28. 
of  weight  of  building  materials,  §41,  p2. 
of  weight  of  farm  products,  §41,  p20. 
of  weight  of  hydraulic  cement,  §29,  pll. 
of  weight  of  Philippine  woods,  §41,  p25. 


Table — (Continued) 

of  weight  of  roof  trusses,  §41,  pi 2. 
of  weight  of  wood,  §41,  p22. 
of  weights  of  merchandise,  §41,  pl6. 
of  weights  of  various  materials,  §41,  pl8. 
of  width  of  walls  for  buildings  of  various 
heights,  §36,  p9. 

Tampers,  Power,  §36,  p34. 

Tamping,  §36,  p34. 
tools,  §34,  p47. 

Tar,  Coal,  §42,  p34. 

Templet,  Stone,  §32,  p31. 

Tensile  strength  of  building  stone,  §31,  p20. 
strength  of  cement  briquets,  §35,  p23. 
strength  of  cement  mortars,  §29,  p25. 
strength  of  concrete  building  blocks, 
§36,  pl2  » 

strength  of  concrete,  Ultimate,  §30,  p27. 
strength  of  metals,  §40,  pl8. 

-strength  test  of  cement,  §35,  pp4,  14. 
stress  on  concrete,  Allowable,  §30,  p25, 
test  of  cement,  §34,  p8. 

Teredo,  §39,  p2. 

Terra  cotta,  Dense,  §31,  p37. 
cotta,  Manufacture  of,  §31,  p37. 
cotta,  Porous,  §31,  p37. 
cotta,  Semiporous,  §31,  p37. 

.  cotta,  Strength  of  bricks  and,  §31,  p40. 
-cotta  work,  Strength  of,  §31,  p41. 

-cotta  work,  Weight  of,  §31,  p41. 

Test,  Apparatus  for  specific-gravity,  §35,  p33. 
Apparatus  for  time  of  setting,  §35,  p25. 
for  soundness  of  cement.  Results  of, 
§35,  pl3. 

Method  of  making  fineness,  §35,  p29. 
Method  of  making  specific -gravity,  §35,  p33. 
of  building  stone,  Laboratory,  §31,  p23. 
of  cement,  Accelerated,  §35,  pll. 
of  cement,  Boiling,  §35,  pi  2. 
of  cement,  Normal,  §35,  p7. 
of  cement,  Steam,  §35,  pl3. 
of  cement,  Tensile-strength,  §35,  pp4,  14. 
of  freezing,  Brard’s,  §31,  p26. 
of  natural  and  slag  cement,  §35,  p36. 
of  soundness  of  cement,  §35,  pp4,  5. 
of  time  of  setting,  §35,  pp4,  24. 
pile,  §39,  p2. 

Sand  for  mortar,  §35,  pl6. 

Testing  building  stone,  Method  of,  §31,  p25. 
cement,  §34,  p7. 
cement,  Purpose  of,  §35,  p4. 
concrete  building  blocks,  §37,  pi  6. 
Difficulties  of  cement,  §35,  p5. 
machine,  Beam-type  cement-,  §35,  p21. 
machine,  Cement-,  §35,  p20. 
machine,  Shot  cement-,  §35,  p20. 
of  sand,  §29,  pl5. 


INDEX 


XXV 


Tests,  Apparatus  for  fineness,  §35,  p28. 
Classification  of  cement,  §35,  p4. 
of  building  stone,  Physical,  §31,  p24. 
Primary  cement,  §35,  pp4,  5. 

Secondary  cement,  §35,  pp4,  24. 

Theaters,  Live  loads  for,  §41,  pl3. 

Thermal  changes  in  concrete,  §30,  p22. 
Thickness  of  brick  walls,  §33,  pl5. 

of  brick  walls  for  dwelling  houses,  Table  of, 
§33,  p27. 

of  brick  walls  for  warehouse,  §33,  p22. 
of  brick  walls,  Laws  governing,  §33,  plG. 
of  foundation  walls,  Table  of,  §32,  p54. 
of  mortar  joints,  §33,  pl5. 
of  stone  wall,  §32,  p54. 

of  walls  for  buildings  of  various  heights, 
Table  of,  §36,  p9. 

of  walls  in  different  cities,  §33,  p20. 
Three-quarter  bat,  §33,  p4. 

Tie,  Morse  patent,  §33,  pl2. 

Ties  for  bonding,  Metal,  §33,  p9. 

Tile  or  brick,  Roof  covered  with,  §42,  p37. 
or  brick  roofs,  Expansion  joints  of  vitrified-, 
§42,  P40 

Timber  footings,  §32,  p43. 

Tin,  Strength  of,  §40,  pl8. 

Toch’s  R.  I.  W.  waterproofing,  §42,  p29. 
Tongued-and -grooved  sheet  piling,  §39,  pi 7. 
Tooled  work,  §32,  p6. 

Tools  for  bending  rods,  §34,  p49. 
for  stone  cutting,  §32,  pi. 
for  stone-cutting  machine,  §32,  p4. 
Tamping,  §34,  p47. 
used  in  placing  concrete,  §34,  p47. 

Tooth  axe,  §32,  p2. 
chisel,  §32,  p4. 

-chisel  work,  §32,  p6. 

Toothed  bonding,  §32,  p27 
Trap  rock,  §31,  p7. 

rock  for  concrete,  §30,  pl3. 

Trass,  Definition  of,  §29,  p9. 

Tray  mortar  barrow,  §34,  p37. 

Trimmings,  Stone,  §32,  p31. 

Trinidad  pitch-lake  asphalt,  §42,  p34. 

Triple  best  iron,  §40,  p9. 

Trusses,  Dead  load  on  roof,  §41,  p9. 

Table  of  weight  of  roof,  §41,  pl2. 

Tungsten  steel,  §40,  pi 5. 

Tuyeres,  Definition  of,  §40,  p4. 

Twisting  machine,  Bar,  §34,  p48. 

U 

Unit  stresses  in  stones  and  masonry,  Allowed, 
§31,  pl8. 

United  States  steel  sheet  piling,  §39,  p22. 
Unsoundness  of  cement,  Causes  of,  §35,  p6. 
Unstratified,  Definition  of,  §31,  p2. 


V 

Veins  in  slate.  Definition  of,  §31,  p9. 

Velocity  and  force  of  wind,  Table  of,  §41,  p28. 
Venezuelan  asphalt,  §42,  p34. 

Verdigris,  Definition  of,  §40,  pl7. 
Vermiculated  work,  §32,  pl3. 

Vicat  needle,  §35,  p25. 

Vibration  on  concrete,  Effect  of,  §30,  p23. 
Vitreous,  Example  of,  §31,  p2. 

Vitrified-tile  or  brick  roofs,  Expansion  joints 
of,  §42,  p40. 

Voids,  Definition  of,  §30,  p2. 

in  sand,  Percentage  of,  §29,  pl5. 

'  Proportioning  concrete  by,  §30,  pi 7. 
Volume  of  cement,  Constancy  of,  §35,  p5. 

W 

Wakefield  pile,  §39,  pl8. 

Wall,  Bonding  of  hollow,  §33,  plO. 

construction  of  concrete  blocks,  §37,  p4. 
Brick  curtain,  §33,  p29. 

Brick  enclosure,  §33,  p29. 

Hollow  brick,  §33,  p28. 

of  concrete  blocks,  Width  of,  §37,  pp4,  16. 

Brick,  party,  §33,  p28. 

Pilaster  in  concrete  building  block,  §37,  p5. 
plaster,  §29,  pi 2. 

Solid  brick,  §33,  p28. 

Thickness  of  stone,  §32,  p55. 

Walls,  Ashlar,  §32,  P21. 

at  angles,  Bonding  of,  §33,  pl2. 

Bonding  brick,  §33,  pi. 

Field-stone,  §32  pl9. 

for  buildings  of  various  heights,  Table  of 
width  of,  §36,  p9. 

for  dwelling  houses,  Table  of  thickness  of 
brick,  §33,  p27. 

for  dwelling  houses.  Thickness  of,  §33,  pl6. 
for  warehouses,  Table  of  thickness  for  brick, 
§33,  p22. 

for  warehouses,  Thickness  of,  §33,  pl9. 
Laws  governing  thickness  of  brick,  §33,  pl6. 
Rubble,  §32,  pl8. 

Table  of  thickness  of  foundation,  §32,  p54. 

Thickness  of  brick,  §33,  pl5. 

to  old  walls,  Joining  new,  §33,  pl4. 

Two-piece  §36,  p6. 

with  brick  quoins,  §32,  p20. 

Warehouse  floors,  Live  load  on,  §41,  pl4. 
Warehouses,  Live  loads  for,  §41,  pl3. 

Table  of  thickness  of  brick  walls  for, 
§33,  p22. 

Thickness  of  walls  for,  §33,  pl9. 

Washes  and  drips,  §32,  p34. 

Water  curing,  §37,  pl6. 

for  concrete  building  blocks,  §36,  p20. 


XXVI 


INDEX 


Water  Curing — (Continued) 

jet,  Driving  Raymond  pile  by,  §39,  p44. 
required  to  slake  lime,  §29,  p5. 

-tightness  of  concrete,  §42,  p21. 
used  in  concrete,  §30,  p29. 
used  in  mixing  concrete,  §30,  pl8. 
used  in  the  manufacture  of  concrete  building 
blocks,  §36,  pl7. 

Waterproof,  Mixing  concrete  to  make  it, 
§42,  p25. 

below  ground,  §42,  p41. 
compound,  Elaterite,  §42,  p30. 
compound,  Minwax,  §42,  p30. 
compound,  Toch’s  R.  I.  W.,  §42,  p29. 
concrete  by  the  integral  method,  §42,  p25. 
concrete,  Classification  of  various  systems 
of,  §42,  p23. 

concrete,  Membrane  method  of,  §42,  p32. 
concrete,  Requirements  of,  §42,  p21. 
concrete,  Stearates  for,  §42,  p28. 
concrete,  Superficial  method  of,  §42,  p29. 
concrete,  Sylvester  process  of,  §42,  p28. 
concrete  with  cement  coatings,  §42,  p31. 
concrete  with  lime  or  clay,  §42,  p26. 
concrete  with  paraffin  §42,  p30. 

Degree  of,  §42,  p22. 

for  ground  water,  §42,  p44. 

Interruptions  in  the  process  of,  §42,  p44. 
Leaks  in,  §42,  p44. 

Necessity  of,  §42,  p22. 

of  cement  mortars,  §29,  p30. 

of  concrete,  §30,  p39. 

of  wet  and  damp  surfaces,  §42,  p45. 

roof,  §42,  p35. 

through  foundations  and  columns,  §42,  p43. 
Waterproofing  compound  for  concrete  building 
blocks,  §36,  p20. 

around  pipe  connections,  §42,  p44. 

Wax  to  waterproof  concrete,  §42,  p30. 
Weather,  Concreting  in  freezing,  §30,  p37. 
Webs,  Definition  of,  §36,  p4. 

Weight,  and  section  modulus  of  standard 
I  beams,  Table  of  depth,  §38,  pl8. 
of  brickwork,  §31,  p41. 
of  building  materials,  Table  of,  §41,  p2. 
of  building  stone,  §31,  pp20,  28. 
of  cement,  §29,  pll. 

of  cement  packages,  Condition  and,  §35,  pi. 

of  concrete,  §30,  p20. 

of  farm  products,  Table  of,  §41,  p20. 


Weight — (Continued) 

of  fireproof  floors,  §41,  pi. 

of  Philippine  woods,  Table  of,  §41,  p25. 

of  roof  trusses,  §41,  p9. 

of  roof  trusses,  Table  of,  §41,  pl2. 

of  sand,  §29,  pl5. 

of  wood,  Table  of,  §41,  p22. 

Proportioning  concrete  by,  §30,  pl8. 
Weights  of  merchandise,  Table  of,  §41,  pl6. 
Well-burned  brick,  §31,  p34. 

Wemlinger  piling,  §39,  p23. 

Wharf  concrete  pile,  Simplex,  §39,  p50. 
Wheelbarrows  for  concrete,  §34,  p36. 

White  Portland  cement,  §36,  pl9. 

Width  of  walls  of  buildings  of  various  heights, 
Table  of,  §36,  p9. 

of  walls  of  concrete  blocks,  §37,  pp4,  16. 
Wind  load,  §41,  p27. 
pressure,  §41,  p27. 
pressure,  Table  of  normal,  §41,  p30. 

Table  of  velocity  and  force  of,  §41,  p28. 
Winter,  Concreting  in,  §30,  p37;  §34,  p52. 

Laying  brick  in,  §33,  pi 4. 

Wires,  Gillmore,  §35,  p26. 

Withes,  Definition  of,  §36,  p4. 

Wood  footings,  §32,  p43. 

piles  compared  with  concrete,  Cost  of, 
§39,  p59. 

Table  of  weight  of,  §41,  p22. 

Table  of  weight  of  Philippine,  §41,  p25. 
Wooden  bearing  piles,  §39,  p2. 

sheet  pile,  §39,  pl6. 

Work  at  night,  §34,  p53. 

Working  force,  Organization  of,  §34,  p3. 
of  concrete,  §30,  p33. 

stresses  for  brick  masonry,  Table  of, 
§31,  p41. 

stresses  of  concrete,  §30,  p24. 
values  of  concrete  allowed  by  various  cities, 
§30,  p26. 

Worm,  Definition  of,  §31,  p31. 

Wrought  iron,  Defects  in,  §40,  p9. 
iron,  Properties  of,  §40,  p8. 
iron,  Purity  of,  §40,  p7. 
iron,  Strength  of,  §40,  pl8. 

Z 

Zinc,  Strength  of,  §40,  pl8. 

Use  of,  §40,  pl7. 


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